Honestly, if the prong collar is fitted correctly, he shouldn't be pulling as much, but I can say from experience that it doesn't even phase some dogs. I wouldn't recommend a harness, unless you're going to reinforce his pulling by training him to pull for weight pull competition or at least to work on drag weights. Go to the Training Section and read up in there about Obedience Training, specifically the "Heel" command and walking on leash. You'll find some valuable information there. You might try looking for a trainer who has experience with Bully Breeds, and maybe sign up for a class, or one on one training and see how he does with that.