I would make one modification to Kim's answer. You want to let him stop when he pays attention to you. Don't worry about how long he is working, if he starts turning his ears/head towards you and paying attention, take a step back and give him an opportunity to turn and face you and rest. If he doesn't take the opportunity then keep him working until he is willing to turn in and face you and wait for direction politely. But if he ever turns his butt at you or invades your space send him to work with a lot of pressure as that is very disrespectful. If you have a round pen to work in that would be the ideal place to work on this issue so even when he escapes he has nowhere to go. But don't just stop him at a random time when you feel he has worked enough, if he gets to stop but still isn't paying attention he will not learn anything. It might take less than 10 minutes or it might take a whole lot more, but I'd watch his behaviour for a good place to stop rather than a timer or just randomly.
It makes it a lot easier for the horse to get away when their neck and body are straight. Try to prevent him from getting straight by always having him bending towards the inside. Read his body language and recognize the patterns of his behaviour before he takes off. Once recognized prepare yourself so you know when he will do it.
I like Brenna's answer.
As well, I would do this. When he takes off, make him run for a full 10 minutes and then YOU decide when he can stop. He will come to find his decisions are a lot of work.
Are you in a smaller pen where he can't go anywhere? Start small and work your way up to a larger pen.
Thank you!! I'll try that!
Ask for lots of downward transitions. When trotting/cantering, ask them to slow down, collect, or do a downward transition before they get a chance to start running away in the first place.