I agree somewhat with the last post. Also, sometimes, if you don't think a horse will canter on the lunge... guess what?
My paint used to do this--I could not, for the life of me, get him to canter in the round pen when I first got him. And when my trainer would go in there, he would run around like a loon toon.
Sometimes it's just the attitude of you. If you know he can do it, and he is not in pain, then there's only one thing left for you to do before he starts taking advantage of this situation--make him canter. You have a whip, use it! Start out with the lightest cue possible, but do NOT be afraid to use what you have. If you always threaten (I'll hit you with this whip! Really, I will! I mean it! Look I'm waving it at you and flicking it at your heels!) but you never come through, your horse will very, very quickly learn to disregard and disrespect you.
Dressage in Jeans
- My blog with dressage tips for happy, relaxed horses, specifically for those who ride dressage in western saddles, no saddles, cowboy boots, or jeans. ;) Also now with cute pygmy goat pictures! :P