Take my word for it, once they learn they can jump the fence and get out, they will do it again and again. My heart horse Sparky jumped out of his paddock form the time he was two until a week before he passed away from cancer at 29. We tried every fence combination known to man. Our place was like Fort Knox, with 5 and a half foot no climb topped with electric, and he still would find a way. I would do whatever you can to nip this in the bud now. All it will take is another accidental escape or two and you (or they) will spend forever trying to keep him up.
He is absolutely beautiful, BTW.
"Keep a leg on each side and your mind in the middle"