Mutt TB/QH - he can be doing about 30 mph in two strides
Yeah, I finally learned the butt/heels down thing. The hard ground is a great trainer
Seriously, get his head up. He can't go forward or buck with his head up. Haul it up, by sheer force. He won't be happy, but he will stop. As long as you've got your heels down and your butt in the saddle, you should have enough leverage.
Had two horses that really learned me good on how to stay on and stop a wanna be bronc. After I left that barn, my form was crap and I had horrid couch seat, but, by god, no force on earth can pry my ass out of the saddle of a horse going nuts.
I respect hard ground, I deceded it was in my best intrest to avoid it.