Another note...he was always ridden bitless but has recently started to ignore the bitless bridle. I had a trainer come out to work with his buddy sour issues once and he put him in a stop and pull bit/hackamore. It helped him a lot! But when I went back into the arena to do some trotting exercises, he was a little too sensitive to the stop and turn and I felt I was giving him mixed signals. I would push him forward and the slightest pull of the reins would stop him from the harshness of the stop n pull. We then tried a bit on him and let him mouth it for a bit. He would not turn or stop with the bit however. (Sorry if that was confusing).
Basically what kind of bit should I be using on him (how do I get him use to it) and what exercises can we try?