On the subject of teaching a horse to canter home politely, I used to constantly ONLY ever canter/gallop away from home on a trail, usually only walking or doing a slow trot back home.
After about 6 months of this, I relised that my mare is a quick walker and eager away from home, and somewhat sleepy on the way back. She was anticipating that all the exciting stuff (cantering/galloping/jumping) happened while going away from home, so going away from home = good.
Relising this, and the fact that she was never homebound anyway, I now canter equally in both directions and shes fine. Food for thought? Shes still more happy leaving home than returning tho. xD.