I would just keep 'changing' directions...I really like doing patterns for a horse like that. My mare likes to wander off the rail, so when she does, I will just take her to an area of the arena that I may have some cones or barrels set up, and do like a spiral around the objects in the same direction (thus keeping the same lead). When I release her she is much more willing to keep the pace, as well as maintain her position on the rail.
Also if he wants to be 'at' the gate, let him drift there, then work his tail off harder AT the area he wants to be. He will eventually figure it out that the gate is nothing 'cool' for him and stop trying to drift there. Horses figure out the 'right' thing quickly when the "wrong" thing involves much harder work!
Good luck with him...
My mare is Walker/Quarter Horse cross
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."