I see a lot of issues here. One, throwing a bunch of new stuff all the time at a four year old OTTB… not generally a good thing for them. Only working them twice a week, also generally not going to work for a young OTTB. These horses thrive on routine. If he’s four and off the track he probably doesn’t know how to jump much, if you’re throwing that at him (amongst whatever else you are doing “trying a million things to challenge him”) he is likely over whelmed. Sorry to be blunt but you and your trainer sound like you are over horsed with this guy. I’d also check into pain – saddle fit, ulcers, teeth, etc. However, a horse that you can’t control is not a good fit for you. I’m guessing if your trainer could have fixed it you wouldn’t be posting. So yeah, I think it’s not a good match. Sounds like a bad situation for you and for the horse. And I don’t agree with Parelli as an answer unless you want to be doing ground work with your horse forever. Quite frankly, anyone who hasn’t drunk their Kool-Aid will tell you they aren’t that great of horse people.