Billy has this wound-thing under the fetlock of one hind foot. When I first saw it last week I thought "scratches". Then I wondered if he caught it on the fence somehow. First I washed it with Selsun Blue. Next day I did peroxide. Then I tried silver spray. It's not getting better. So now I'm using a fungicide cream. I can't put his boot on as it would be right where the sore is. So, scratches or wound??