Do LOTS of cantering! My horse used to be terrible about that. I have been using Clinton Anderson's Method and on of his exercises it to put your horse at a canter and make them keep that gait up for 10 minutes! If they break into a gallop, shut them down with a one rein stop, and if they slow to a trot, push them back into a canter.
I love circles. My mare hates them because they make her work. LOL. I tell everyone circles are your best friend.
thanks for the article! im leasing a western/english mare and i have that problem of her going faster along the long side of the rail. and i dint want to be yanking on her mouth to slow her down. so i did alot of jogging circles and trotting circles. ive heard extending the jog works too.. anyone know if it does help?