I take a bucket of warm water and a sponge to the really tough mud. Once it is softened up it comes right off. I'm big on keeping my hoses drained in the winter, so I just carry out a few gallons of water from the house. If you board, you might just bring a few milk jugs of hot water and a sponge with you from home.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France