He's not scared. He's just got your number. He knows you can't make him. He knows you can't hold him.
1. More turnout. If a horse has that kind of energy to burn, they need to have more time to run and play to blow it off BEFORE any kind of work can begin. He also looks to be in very good weight, so I wonder if an adjustment to his concentrates isn't also in order.
2. Enclosed area. Once they learn they can leave whenever they want, you're stuck. Work him someplace, where if he does get loose, he can't go far.
3. Longeing Cavesson. You have no control longeing in a halter. They can whip the head around and they are gone. A longeing cavesson applies pressure to the sensitive nose. A horse hits the end of that and they'll usually think twice about trying it again. The term is called 'leverage', and right now, you've got none and he knows it.
4. Wait for experienced help. You're in over your head at this point and a habit is being created that becomes infinitely more difficult to correct the more times it is allowed to happen.
5. Research. I'm not entirely convinced you do know how to longe, or that you've been taught properly...per the outcome with this horse. So grab a book on longeing and start learning on your own, so you can identify if the person teaching you firsthand knows what they are doing.