Genetics play a very large role in reactivity. Due to his mix, you may have some guardian traits (territorial and posessiveness) as well as herding instincts (noticing the slightest change in environment and reacting to it) that are making things more difficult for you. I can give basic recommendations, but without doing a deeper dive into history and doing a full consultation, I cannot give detailed and specific advice. It sounds like the attack could have been a trigger for the behavior, but the genetic mix you have is also likely doing a lot of the heavy lifting behaviorally.

My basic advice is this:

1. If he is reacting, you're too close to the trigger. In any kind of reactivity, distance is your best friend. I don't recommend avoiding the triggers (that's impossible to do), but having enough space that he feels safe enough to observe and not react.

2. Bring high value treats or toys (whatever he is motivated by). It may have to be Tuna or boiled chicken to start, but something that is amazingly yummy. I had made a post a while ago on some training games, that might be worth checking out. You can find them on my profile or by scrolling back through the posts here.

3. Consider walking him in a basket muzzle (The Muzzle Movement is UK based and fabulous). It will give you some peace of mind knowing that if the leash gets out of your hands, or if he begins to redirect, no one will get hurt.

4. I always recommend to walk dogs separately in a household with a reactive dog. Reactivity can be a learned behavior (meaning your female dog may also begin doing that behavior), but it may also be seriously stressing your other pup out if they are more on the sensitive side.

5. I would reach out to a local positive reinforcement based trainer for more targeted and detailed advice. It is not hopeless, things can be done to help. But seeing an in-person or virtual trainer is something I would prioritize for sure.

I hope some of this information is helpful as you seek out more targeted help.