You need to stop being afraid and just tie him. Just don't tie him as short. Even a good horse will have problems if they are snubbed up to something to tight. I had a mare years ago that for no reason what so ever would set back and probably flip over a dozen different times. Yes, there is a risk and it is not a good habit. Before all these fancy new clips, I used what was called a Be Nice halter, it was a rope halter on a pully type system and hooked to the piece that goes across the pole were little nubs, so that when she pulled back (leading or tied) it would put pressure and when she would come forward and relax it would release the pressure. She wore it for 6 months or so and have never had a problem since. You could also try using and inner tube. They used to do this with the TB's that I worked with. We would bring them in as long yearlings (never worked with) and in a round pen they would have inner tubes tied to ropes which were tied to the posts. We would then tie their lead ropes to the inner tubes.. The tube gives when they pull back, they would leave them tied for a couple of hours at a time.

You just need to make sure what ever equipment that you use it is in good condition and is strong, If they consistantly break things they will learn that the harder they pull it will break and thats when they can do serious damage. When they have that much force and energy and then it breaks loose.

Good luck in what ever you use, but just get back to tying him soon. The measure of a good horse is one that stands tied quietly for as long as you need them to .