Originally Posted by Seahorseys
also, as far as the whip goes, the horse can sense if you are bluffing. He trusts you are not going to hit him with that whip right now. So the whip, in a sense, is your legs in the seat. The line, your reins. It would be like saying while riding, "I'm going to ask for a canter, but i'm not really going to ask for a canter." A swishing, raised whip is both an ask and a warning. A pop of a whip is a both a stronger ask and a warning. A smart, swift well-placed graze against the hocks or bum is the last ask as well as a consequence. Your horse will learn that he'd rather take the first ask if you do, in fact, follow through consistently.
To add to that.... get big, jump up and down, stomp your feet, growl, get low to the ground while moving towards the horse, crack the whip... etc.
Walk towards the horse with purpose. Sometimes a poke on the shoulder with the end of the whip helps. As Seahorseys said, sometimes one swift crack to the rump goes a long way.