Join Date: Jul 2010
Location: Jacksonville, NC
This is dangerous and I would highly suggest going back to basics with this horse. Most likely it's you (99% of all mistakes a horse makes is due to the rider), since you said he doesn't do this with your trainer. I would stop jumping and work on ground poles. Trot poles and canter poles, really working on keeping your horse in front of your leg. Then move onto raised cavaletti, then small cross rails, etc. Go back to basics. All the whips, spurs, and kicking won't make a difference if the basics aren't there for both of you.
Work on your half seat/two point, really making sure you are balanced and not leaning on the reins. That way when you are jumping, you're not throwing him off balance, or jerking him in the mouth inadvertently.