Just one hock? I think Listerine is an old Pony Club remedy, but I’ve never tried it. Listerine is supposed to kill bacteria in the human mouth, but mites are little creatures related (I think) to spiders, and Listerine probably won’t have any effect. If it gets bad enough, call in the vet. You want to stop the mites, or whatever they are, from spreading. Good luck!