He doesn't canter on a line. I've had an English trainer, a western trainer, our BO and myself all try, and as soon as we ask him to pick something up faster than a trot he stops and turns in to face us. You can see it in this video
Btw that's not me, that's our western trainer.
And any time there is a horse in the arena, the gate is closed. But he'd stand there all day and wait for someone to open it no problem. I've sat there on top of him and fought with him for fourty five minutes, circling and backing and sidepassing any way but forward or standing still and he still will NOT move back into the arena. But as far as working him that hard....thats how he made a living, that was his whole purpose in life was to work up that kind of sweat, so in this case I don't think that would make a difference