Are you sure his behavior is aggression vs confusion? Perhaps you are applying too much pressure.
My "roundpen" is nothing more than a single rail fence. I sometimes use it as a drylot. I've never had a horse break out or attempt to break out during lunging or groundwork sessions. My one mare has figured out how to open the gate, and she lets herself out, but that is very deliberate.
When I lunge my horses, i want relaxation and forward movement. I don't push for a gallop. Some cantering is okay, sometimes i get a gallop with a more nervous horse, but that means I need to reduce the pressure. More is less in this case. With youngsters, i like to start with walking a circle. A couple circles each way, that's all for the first session. Next session we trot a few circles, if they do well at a walk.
If the horse is dominant, i correct this on the lead. Backing, circling, and yielding the hindquarters can all be done in hand. For a more difficult case, carry a stick if you need one. You can establish yourself as herd boss without ever setting foot in a roundpen.
Carry a whip with you, ask him to yield away from you before he gets dinner. Or make him wait for dinner. If he is the type to charge, carry a whip with a lash and stand on the other side of the fence. Make him wait for supper. When he stands quietly, let him eat.
Too many people think they need too much force. For example, i like Clinton Anderson, but i do not agree with the way he runs his horses. Part of it is showmanship, but i can get the same results with less effort. Of course, i don't need a horse to spin when changing direction. I like a calm, quiet, relaxed change of direction. I want my horse thinking, not reacting.
As for my background, I'm used to working with hotter breeds- your Arabians, thoroughbreds, and pasos. I do enjoy a good quarter horse, they tend to be easier to train and more forgiving.
Most horses do not try to "leave" unless they feel completely overfaced. Your goal as a trainer should be to recognize when your horse is getting overwhelmed, and know when to back off or reduce the pressure.
I did have one horse try to leave his stall in the way you described. He reared up, stuck his feet between the boards, pulled his feet back in, then came down. (I did add more boards so there weren't any accidents). I believe knightrider on here has a mare who did the same thing in the horse trailer. The first horse had severe seperation anxiety, the second had a phobia of trailers. It is likely your horse will repeat the behavior if pushed into a panic.