Need advice on overmated Call Duck

I have 9 gray call ducks, 7 girls and 2 males, all mating age. One of the males was hatched out last summer by a big duck with 2 of her other eggs and thinks he is a big duck and doesn't even mate with the other call ducks. I find him on the backs of the other big ducks trying to mate.

So my problem is that the other male mates with all of the girls but he particularly likes to mate with one to the point that her head is actually getting a raw spot. She also doesn't appreciate his advances but he is bigger and stronger. The other girls have a few feathers missing but nothing bad. DH tried to bandage her head, but it didn't even stay on 2 seconds. They free range during the day so boredom isn't the problem. I hate to keep him locked up since he is just doing what drakes do, but I also hate seeing her little head looking so bad.

Right now, I have her in my fenced in garden with some neosporin on her injury. Any suggestions would be appreciated.

Thanks