On a very determined dog a shock collar will not be very effective and on most pits all it does is make them mad. If the dog was bred from a line of agressive dogs the behavior is there and there is not much that you can do to change it without professional training. That is one problem with rescue dogs, the background is not known and the early training/socialization is very important.
Now I'm not saying that it can't be done but I believe that it will take someone that really knows their stuff to do it.
Now I'm not saying that it can't be done but I believe that it will take someone that really knows their stuff to do it.