You might try doing transitions from walk to trot, and trot to walk. About six strides, then change. The idea is to develop communication through the use of you seat, so ultimately, very little hand is needed. If you do this exercise on a twenty-meter circle, the difficulty of traveling the circle will help slow him down. Change direction often to keep him from being bored. I will say what I’ve heard Charles de Kunffy say to a horse, “Oh, did you think I said trot, I said walk. Oh, did you think I said walk, I said trot.” This conveys the back and forth nature of this exercise. Keep in mind that it will take many, many such transitions to have an effect–a hundred, maybe. Basically, you are teaching him to wait for your instruction. This message may not be in his nature or his previous training. A second exercise is to spiral in and out of a twenty-meter circle, doing a leg yield in and a shoulder in out.