The reason he does this is that his owner, who rides him everyday after I do, leans too much to the inside, pushing him toward the rail more. Luke, obviously, takes this as a cue to move outward and squish himself up against the fence. Now he does it just as a habit, as his owner is constantly asking him to do this, though not purposly.
So far I've tried leaning to the outside to push him off, using my outside leg, opening my rein.. everything. While he listens most of the time, since his owner is back on him right after me, there is no progress. Everytime I get back on him, he's doing it again, and I've got to ask him off. I'm starting to think there is no way I can break his habit! Every time I stop asking him off, he just goes back to the fence. I mean, right on the fence, as in my foot will hit the fence.
I really need help, because, honestly, I'd rather not have to be on him all the time about getting off the fence.. :\