I taught him to rear by having long lines on both sides of the halter (like reins would go) and asking him to go forward by clicking or wisteling and for me I say "levade". So he wants to go forward but Im holding him back with the lines and so usually the horse wants to back up, don't let him back up with your crop. Then when they can not go forward or back they decide to go up!
Usually they are confused at first but be patient and reward a little try. My horse knows not to unless I ask him to and I only ask him to when he has long lines on. I've never had a problem with using it against me because (for my mini at least) it takes extra effort and he would rather not unless I ask.