everyone is saying a fly sheet won't work, BUT: I'm here to disagree.
I have one on my horse and it works wonders. somehow it keeps him pretty dry too. I take it off, and underneath... amazing cleaness.
Right now it's really muddy in his pasture too. I only get out to the barn once a week allot, and so he's only groomed about once a month, and he stays super super clean with the fly sheet!
A shedding blade can get even the most mud covered horse ever, clean in a few minutes. I groom my horses primarily with a shedding blade in the spring, cause it removes the hair and the mud at the same time.
Heir To Liberty || aka Liberty || Bay Arabian Gelding || Dressage
Moonlight Mystique || aka Mysti || Chestnut Arabian Mare || Western
Regent Psyerra || aka Psyerra || Chestnut Arabian Filly ||