The easiest way to do this is off of a wood fence or arena wall. Make sure that your legs are anchored and you have unobstructed access to the horse. Your goal should be to longe the horse up and down the rail. At first you will find this difficult because the horse will drift out from you because they are not comfortable with your new height. With some time, you will find that you can bring the horse right up to you.
Energy is an interesting concept.
It sometimes takes the rope to run into the horse for them to understand this energy concept. Once you have the techniques down with a 12 foot lead rope you are ready to move up to a 22 foot longe line. And once you have these techniques mastered with a 22 foot longe line, you can move up to a 45 foot longe line. Available in 22 or 45 foot length. Leather popper at the end.