ONE REIN STOPS!
Teach him a very good 'One rein stop". Do it right and the he will learn that when you run a hand down a rein, he has to stop. You can fix any of these chargy horses -- even bolting runaways.
It takes about 3 or 4 sessions to get this done right on a horse like this. I've done it on more than a hundred of them.
When you pull on both reins at the same time, a horse can 'push back' or can just tune you out and keep going. They cannot fight a properly applied one rein stop.
I have to get a big set of trail horses ready and will be gone all day so I do not have time to look it up, but I put up a post long ago titled "One rein stop -- our way". It tells exactly how to do it without having any negative repercussions. Just do an advanced search.
This is one of the easier problems to fix.