I use a chunk of grill cleaning block, or slicker block after the
paint has had a week or so to dry, IF I actually try to remove it.
Mine tend to stay so black with mud the marks don't show through...though I have
had neighbors comment on the same horse going to the sale so often, and always
coming back home...
Best thing I've found, esp. when that winter hair
gets started is a cat slicker brush. First brush with the hair, then
brush against. Any ruminants will be gone
after the next rain.