Like I said, if you can get him into an arena and chase (playfully) some of his youthful energy out of him he will be less likely to be a problem when you are trying to teach him to lead. If he has a buddy, you might bring them out together and have them run and play with some encouragement from you. Just keep it fun so he doesn't learn to fear you -- remember we are the predator they are the prey. (Horse mindset)