Leash aggression is NOT unusual. His responding to the choke makes me wonder how much is actually aggression and how much is learned behavior. But please do not ever hand your dog off to someone. Had he flipped at her choking up on him, you would have seriously risked things being worse AND him fearing strangers.
I work on serious distractions at home once a dog is taught "leave it" and "look at me." I have had people bring bitches in heat over, bounce balls, throw meat next to the dog. Once you have that brain path totally locked into responding to the commands, it does help it transfer to situations away from home. Next I'd work just in front of YOUR house with people you know to use as training. That way can do it over and over and over til he gets bored with flipping and being made to ignore.
Most of my dogs and rehab rescues, once taught "leave it" and "look at me" solid, 100 percent, at home, can be stopped before they escalate on walks and around other dogs. Remember, my breed is Rottweilers. Rottweilers who are German working lines. So while I totally GET it is distressing, but you have the option of picking his butt up at least
I sincerely would even consider adding a head collar to his leash or a basket muzzle. Some dogs, once they KNOW they cannot do anything, will give over and let YOU be in charge and protect them.
Aggression toward Passing Dogs
The focused attention exercise, developed by expert trainer Linda Newsome, is ideal for handling your dog around other dogs. You teach the exercise first in other settings, but soon will be able to use it anywhere and know that you can keep your dog's attention on you and off anything else. It's a humane way to be in complete control of your dog-especially when combined with a head halter until the dog is totally reliable.
The first requirement for using the focused attention exercise is to find a setting where you can provide your dog with a safe personal space. Don't ask your dog to give you full attention and ignore everything around the two of you unless it is safe to do so. Part of what makes this work is for you to become someone the dog can trust to look out for safety. A dog whose experience builds the expectation of having to always be on guard has good reason to be aggressive. To resolve this problem in your dog, you'll have to take over the job of safety officer.
Have treats on your person (later you may use a toy instead, but it helps to start with tiny, tempting treats - lots of tiny pieces), but keep them out of the dog's sight. To initiate the attention sequence, say "[Dog's Name]!" and YOU MOVE ABRUPTLY away. If you want to say "heel" or "come" or "front" or "by me," that's fine too. The main thing is, say the dog's name - this is going to become the cue for the dog to give you eye contact - and then MOVE.
When your dog moves with you, quickly PRAISE. This is when you would use a clicker if you wish, but a word of praise is fine, too. Then instantly whip out a treat and give it. Do not show a treat until you are ready to give it. This prevents the sight of a treat from becoming, in the dog's mind, part of the cue to listen to you. When you give a treat, align it between the dog's eyes and yours. You want eye contact with each treat. Soon you'll notice your dog seeking your eye contact even when you don't say the name. Always praise this, and sometimes give a treat to reward it.
You're not done. When you do this sequence, always do it at least 3 to 5 times in a row. That means each time you 1) say the name, 2) move, 3) say the praise word, 4) whip out a treat and 5) give it. This doesn't necessarily require much space, since you want it all to happen very fast and the movement is not over a great distance. You can move one direction the first time, back the other way the second time, etc. But always do at least 3 to 5 repetitions in a row before you release the dog's attention. This is what conditions the dog to SUSTAIN attention on you until you release it.
Practice everywhere, and don't be quick to discontinue the treats. Keep them up at least occasionally forever. Because you're not dangling the treat in front of the dog before giving it, you're conditioning the dog to respond even when you don't have food. You want to make the behavior quite strong and build the importance of other rewards (praise, petting, play, toys, etc.) in the dog's life before moving away from food.
Praising before each treat or other reward will make your praise more motivating to the dog. Eventually you'll be able to praise for the behavior you're rewarding, and use your voice as a bridge while you walk to the treat jar or refrigerator at home. The dog will understand the treat is a reward for the behavior you praised. In this way you can reinforce behaviors you want to see more of – such as coming quickly to your call -- when the dog does them at a time you weren't expecting to do a training session.
Do not postpone intervening in your dog's aggression issues with the focused attention exercise, a head halter or muzzle, and appropriate expert help in-person. These problems do not magically disappear. Dogs don't just outgrow aggression. It usually gets worse unless the right interventions are done.
The sooner you start working on the problem, the greater your chances of success. Every single time the dog acts on the aggression, the habit gets stronger. It will then take a longer period of time and more reconditioning sessions to change the habit-if it can be changed at all. These problems often emerge in adolescence. This is a volatile time for dogs and a period of their lives when time is running short for you to effect significant change in the dog's adult personality. There is no time to waste!
If you immediately start the focused attention exercise every single time you spot another dog on outings with your dog, you'll soon find that your dog automatically looks at you when another dog appears! In many cases, you can actually turn a problem and a weakness in your dog's temperament into a special strength! This has been noted over and over in humans who put a great deal of effort into overcoming some disability or disadvantage in life, and you can do the same thing for your dog.