I'm *thinking* it's in part due to traffic here. We live on a farm, and not only are there 5 related households, but the main home has an invalid who gets a large number of nurses and the like coming over to check on him.
Before this, I let her run as she wanted, which would let her go hunting rats in the barn and the 3 chickenhouses (I know she's a terrier, and ratting is one of those things she does). She never shows aggression towards her "pack" - My household, or anyone that lives on this farm.
She's up to date on her shots, so it's not rabies/distemper - not an OBVIOUS medical issue.
A small look into her personality - she was raised from puppyhood with small kids, which is generally a no-no with her breed. And when I got her, my daughter was in diapers, yet my daughter was her master in her eyes. My daughter can't go anywhere without Minnie trailing.
I've tried something basic - putting her on a leash, then walking, changing direction and stopping at random times to kinda force her to watch me and where we were going (a trick we used on the pug we had) but she's a lot more difficult to train than my pug was.
I'm answering these together because they're both examples of aggression. "Aggression" is a very broad category, ranging from Ember's barking at dogs to Minnie's biting of people. The origins of aggression vary a lot, from being undersocialized and just having poor doggie "social skills," to over-reactive possessiveness, to extreme fear caused by abuse or a feral childhood.
Aggression issues are complicated, often deeply ingrained and vary from dog to dog. They cannot be treated by someone over the internet; they require personalized attention from a professional. However, for anybody thinking about calling for help, here is some information about the methods to treat aggression that might be helpful.
CONFIDENCE AND RELAXATION
Almost all aggression has its roots in fear of some sort, in the "fight or flight" reflex. So, the first step is to alleviate as much of your dog's anxiety as possible. An excellent start is to to establish a regular routine with your dog of feeding times, regular walks, relaxation time and play. Set yourself up as a strong leader - do not let your dog demand your attention on her terms, require polite obedience in return for food or access to toys or affection or walks, and so on.
All dogs are instinctively more relaxed in the presence of someone they regard as their boss. To be a leader of a pack is to have the responsibility of protecting the pack and looking after it. If someone else is the pack leader, that means the dog doesn't have to worry about all that and can chill!
This covers everything from the Cesar Milan light, instant pop on the leash to much harsher methods involving yanking hard, "hanging" the dog with the leash and shock collars.
Don't use these methods. They can work, to an extent, when done by someone with perfect timing and expert dog-reading skills. You don't have those skills. Furthermore, most trainers who will take your money to use these methods don't have those skills either.
Even when done properly and perfectly, there's two problems. First, they can have unexpected consequences down the line - the better behavior fades, or more commonly, the aggression come back worse than it ever was before. Two, they don't actually fix the real problem, the attitude of the dog. They may inhibit certain behavior, but the emotions that triggered the barking/biting are still there under the surface, waiting.
COUNTER-CONDITIONING and DESENSITIZATION
Usually shortened to CCDS (or DSCC), this uses Pavlovian techniques to replace a dog's fearful association (with other dogs or people), with a happier association (steak!). Put very, very simply - you wait until your dog sees what sets it off (but at a distance that doesn't provoke a full fit), and then give your dog something awesome (steak!). Once your dog is pestering you for food whenever that thing shows up, you can make the distance closer. Repeat until your dog is fully associating the appearance of that thing in any situation with the possibility of awesomeness.
Obviously, there is a lot more technique to this than just that paragraph. Please look for a professional in your area with experience in CCDS. If you need help finding a reputable trainer in your area, feel free to write me at email@example.com and perhaps I can help.
CCDS, if done correctly and consistently 2-4 times a week, typically takes 2-4 months. Periods of 6 months or more are often reported, though I suspect those people aren't consistent. And while I haven't had the chance to try it, research would seem to indicate that you could actually get much faster results if you were willing and able to do it a lot, every day, for a couple of weeks.
Keep in mind that doing CCDS "correctly" means not letting your dog be exposed to whatever sets it off, except in controlled training sessions, for the duration of the rehabilitation program. That... is challenging. But if you can manage it for a couple of months and put your time in, you can fix most of your problems.
CONSTRUCTIONAL AGGRESSION TREATMENT
The unfortunately named "C.A.T." program is a new-ish procedure developed by Dr. Jesus Rosales-Ruiz, PhD. Put simply, you could call it a "Fake It Until You Feel It" program. The basic premise is that what a dog really wants when it barks/growls/bites is to make the scary thing go away. So why not use the going away as the reward for the behavior you want?
The dog is exposed to the thing that sets it off (the "trigger"), at a distance where the dog's reaction will be mild. The trigger stays there until the dog does something that doesn't look like aggression - turns away, yawns, sniffs, etc. At that exact moment, the trigger leaves. Repeat over and over again, at lesser and lesser distances. The dog learns that not acting aggressive is what makes the trigger go away.
There's a lot more to it, of course, but a really remarkable thing happens. There's a point at which the dog has been offering friendly-looking behavior to the trigger so often that it actually becomes friendly. It's actually quite miraculous when you see it happen.
The trouble with CAT is that it works best when done in big chunks of time over a compressed period, like 3-4 eight-hour days in a row. That's a big commitment of time. Add onto that that you need a lot of volunteers. It's not enough to get the dog to be friendly towards a single person or dog - although you can certainly do that - but if you want that friendly attitude to generalize to all dogs or people, you're going to need a lot of volunteers over those 3-4 days (say, at least 5-6 people or dogs).
C.A.T. qualified trainers are pretty rare right now. (I'm one, and I think there's only one other in Los Angeles, though there's a very good one in Santa Barbara.)
On the other hand, when it works, you can totally turn a dog's attitude around in a long weekend, which is just miraculous to see.
If Ember will lay down down voluntarily when you tell him to, it's not an alpha roll. Anything that keeps him calm as much as possible in the presence of other dogs is good for him - he's learning that being calm is an option. Feel free to place a firm but calming hand on him once he's down. Just don't force him down - your instincts are good on that count.
I think CCDS is probably your best bet. Find a trainer with experience in your area. Keep in mind that you may not need to get him to the point that he loves other dogs in all situations - if he learns to associate dogs at a moderate distance with great rewards, that may be good enough for you as long as you can usually keep some small distance between him and other dogs.
Yeah, with a Jack you're going to get a lot more progress using treats. They're "headstrong" dogs - all that means is that the old-school methods of jerking them around on leashes don't work that well. But Jack Russells usually respond really well to treats.
If you want her to pay attention to you as you walk, start by making some small "Tsk" noises as you go. When she looks up in response, toss her a tiny little treat (the size of a pencil eraser is fine). Repeat a few times. Once she's figured out that game and is anticipating the "Tsk" sound, stop making it. When she looks up at you on her own as if to say, "Hey, why aren't you making that sound that means you'll feed me?", toss her one of the treats. Now you start tossing them whenever she looks up at you on her own.
During this you're still making random course corrections, but usually you'll precede them with that little "Tsk" noise until she's watching you often enough that it isn't necessary.
Once she's looking up at you ever few steps, start tossing the treats less and less often. Don't fade too fast, but over a few days, you should be just tossing a couple over the course of the whole walk. Eventually, you won't need them at all.
In addition, use the Loose Leash tips from my earlier blog post, and she should be paying much more attention to you.
However, all that said, I don't expect this will make her less aggressive to strangers on her own. For that, I think you're going to need one of the actual methods I mentioned above. However, for a Jack who is food motivated (if she is), you might have some luck modifying the CCDS by making sure an strangers are given a few pieces of jerky or chicken to toss on the ground whenever they pass by her (not directly approaching her and not not leaning down to give them to her). Put a basket with the treats and an explanation by the front entrance gate to the farm or something. If every time someone walks by they're tossing a treat on the ground for her, she'll probably start to feel a little better about strangers over all.