I know this is really old, stumbled on it searching for grooming blocks but since noone really said anything about the caked mud, in case it's not abswered somwhere esle already here goes:
Get a sheding comb for dogs, best known is Furminator but any 10x cheaper copy will do.
I live in one of the wettest places there is, rains all year and in the winter, mud+winter coat is just ace! I own a tack and pet shop so I tried everything we sell, and that was the miracle solution.
Hope I helped!
Have a nice winter!
PS: to scrape the accumulating mud+fur cake on the comb just carry a stiff brush on the other hand to brush past it every few swings.