A lot of the problems with pit bulls lie in the "backyard breeders" who were breeding unreliable lines- human aggressive lines which is very different for pittys. How you bring up a dog can only do so much against natural urges. For instance, you can't stop a border collie from herding things, it's just natural for it. For unreliable lines natural means things like fear aggression, high prey drives etc. things that cause bites.
I'm not saying your dog is unreliable at all. But what I'm just saying is that there is a big problem right now in the cocker community and it is best to let the professionals figure it out until you think about perhaps getting into hobby breeding. You may want to talk to a few breeders within your area and get their imput, I can defitently get some contacts for you if you are interested.
I just know what it's like right now to have to fight for a dog with a bad reputation. I'd hate for any other person or breed to expierence this. I currently have a waiting list of 58 pit bulls trying to get into my foster program. Most will be put down this week, and I'll get another 25 next week. With the cocker community, they are starting to see this too. No one will adopt our breeds because they think they are nuts (thanks media!).
PS. How old is your dog?