I once had a trainer have me put my horse in a circle at a lope and when he rushed or threw his head he immediately got pulled in the other direction and kicked back up into the canter. They don't want to have to work that hard and usually quit rushing...for a moment:)
As for your canter depart, I don't really have anything except you probably already know to not lean forward and don't look down at your lead because it puts too much weight on the front hand. I would just think forward, forward, forward and really drive with my seat and leg. Take my advice with a grain of salt though...I've been riding for awhile, but am by no means a pro.
Good luck...hope it works out.