When I first got Sarge, he had a non-healing open wound on his withers, a souvenir from surviving an attack by a stallion when he was four months old. The stallion ripped most of the skin from his back and chest, as well as damaging muscles in his back. Everything healed up except an open area that was larger than my hand when I first saw it.
Here's how it looks now:
That's the good news. The bad news is that this nice, tight scar gets flaky and itchy, leading Sarge to roll and scratch himself on trees until he scuffs it open again. It's nowhere near as bad as it was at first, but I'd much rather he didn't skin it up at all.
My vet had me treat it with topical nitrofurazone ointment to get it to close up. I can keep gooping it up with that, but the stuff is nasty-slimy, attracts dirt, and requires I apply it wearing nitrile gloves. Corona and Bag Balm also tend to sit on the surface and collect debris. Horseman's Dream works well, but wears off too quickly.