horse is getting bitten

Question
I have a strange question. I am an experienced hunter/jumper rider with a little dressage background. I just purchased a 3 year old warmblood and am starting him dressage (under professional supervision). He's a wonderful boy, and has a great personality and work ethic. The problem is when he goes out in the pasture next to other horses. He goes out with an older gelding and a pony, and he gets along great with these horses. But he constantly wants to play, and the horses he's with will run him off or ignore him (they dont have much play drive). But the horses across the fence like to play. So the problem is this: my horse keeps coming in with huge bite marks (the size of my hand sometimes!) The severity of the bites are getting worse, deep bloody, hamburger looking bites along his back and sides. I thought he'd learn to leave these horses alone when he got bit up the first time, but he's been next to these horses for a couple months now and he's still coming in torn up. He yields to pressure beautifully when I push him over, and during his ground work, so why wont he yield and get out of the way when playing with other horses? Moving him or the other horses isn't an option at the moment (I'm boarding him) and I'd hate to say he can't go out in the pasture anymore, but I don't want him to have all these scars and I'm afraid he's going to really hurt himself one of these times. Have you ever had/heard of this problem before and do you have any suggestions?
Thanks!

Answer
Hello Jessie,

I would suggest stringing electric wire across the barrier between your horse and the biter.  Otherwise, you would have to move him or keep him in.  Obviously the play instinct is stronger in your horse than the self defense instinct.

Or.....are you sure it is that horse that is biting him and not one of those inside his pasture?  Have you seen this happen?  In any case, you certainly have to do something to stop his injuries, even if it causes you difficulties.  Electric wire would be the simplist if the owner of the property agrees.

Happy riding,
Dorothy