I knew a mare who did the same thing. I Got on her, with her head bent, she tried bucking and I dug my inside leg into her, turned her head and cropped the heck out of her butt to get her spinning in a really tight circle really fast. They can't really do much if the circle's tight enough. As you're spinning, you'll feel the horse start to tire and slow down. as soon as you feel this, urge them and make them spin REALLY fast for a few seconds then let them relax. if they try to buck again, spin again (I suggest the other direction so you don't get too dizzy ^^) and repeat the process. Spurs are good for this so you don't have to kill your legs in an effort to move his hind end around. Make him think that bucking is the worst possible thing he could ever do and make him understand that whenever he does this, he has to work hard and get dizzy. lol
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