OTTB training advice needed!

history, i got my 8 year old Ottb gelding November of last year, he came off the track that April/June. When i got him, he was underweight, he had no muscle, and absolutely didn't want to work (who would??), Fast forward a couple months he's gained weight, we start training to build muscle, light exercises, etc. He progressed amazing, took everything in stride, he is truly such a willing horse that is always wanting to please... at home, which is where the advice comes in..

At home he is an angel, walk, trot, canter, jumping, stopping, all the things. but off property, at shows he's a completely different horse (obviously track brain) he will take off and race the other horses the whole time, do anything to get away from my hands and seat just to run around. what can I do to work this out? i don't want to continue to show him to "work it out over time" because I'm afraid Itll do more harm than good. pain is ruled out, and again he's a different horse at home, so how can I enforce that off property not just at shows but anything in general. He is not dangerous in the slightest.

To add , i haven't "shown" him off property over fences due to that, but my goal is for him to be a jumper, he loves jumping, but again loses his mind at shows and just wants to go go go. I've had him for a year, and hes been to 3 total shows, 1 before i got him and 2 with me. when he's in the arena alone, he's great, its when other horses come into play he doesn't care a lick about what I have to say.