You need to keep Jack out of the yard until the problem is resolved. Every time he practices leaping at the fence, he gets better at doing it. If there’s any way to block the area from him, he’ll have less of a chance to reinforce the habit. You should find other ways for him to get out and urinate without guarding the fence. If that means you can build a separate section away from that side of the yard, that’s great. If it means he may have to do his business on a leash or on walks for now, that’s another option.
Next, you should engage in a relaxation protocol. I recommend the Karen Overall Relaxation Protocol. What this does is teach your dog to stay still while more intense things are happening around them. You would then take those skills out into the yard with them on their leashes, probably one dog at a time, and train them to sit and stay calm while people are passing. It’s essential that you reward them for staying calm when people pass. We need to change your dog’s emotional association to people passing by. That means giving lots of treats and pets — or whatever their favorite thing is — whenever they exhibit good behavior.
Instead, use high-value reinforcement for staying calm in the presence of the trigger. This process will take time and patience, but it’s absolutely possible to change Jack’s relationship with the backyard fence. Avoid using things that promise to be quick fixes. Using force or something that creates pain, like an invisible fence or shock collar, can give you a short term change, but the emotional association toward the trigger is likely going to get worse. Jack will just become more concerned about — and afraid of — people passing by, because he’ll associate them with punishment.