I see there are several threads on stopping a horse that is bolting for the barn or just out of control. I advocate the emergency one rein stop most of the time. Many times you don't have the space or the balance needed to do this maneuver.
I saw this video several months ago and started practicing it with my horse. Its a fabulous tool to have in your horse toolbox, so I'm posting the video again.
It doesn't start until about 3:20 into the vid so be patient