Have you thought about just muzzling and taking him off the lead. A lot of dogs react like yours (mine still does at times, but only on the lead) as the lead means they cannot run away if they feel nervous, so feel the only thing they can do is fight or submit. Now I no longer need the muzzle. I tried a harness and although you physically have more control it allows the dog to pull more. My dogs use a half check collar, when I need to do a correction (which is usually when I walk past a dog!), I firmly but quickly pull the lead upwards or to the side (never backwards as this can cause them to pull forwards) and this "snaps" them out of it. When you see another dog you need to try to distract him and not allow him to focus on the dog, this is where using a half check collar has helped me. Also if you are physically having to pull him back, which you will have to with a harness on, then you are fueling his fight. He's pulling and your pulling. I'm not an expert, but with 2 problem rescue dogs, I've worked with a great behaviourist and we've solved many of these problems. I do find that taking my dogs to another park helps as when they know the area they feel more sure of them selves. Why not try a different place with a different method of controlling him? I understand how you prob feel, it's been a really tough year with my two and it's really good to be coming through to the other side! Good luck x