My Fleabitten Paint is forever a lover of fine sand. Silty stuff is her favorite. She's a total connoisseur of good, sticky, tiny-particle sand unique to certain wind-blown, trampled areas. She wouldn't dream of rolling on grass. If I refuse to let her in the churned-up paddock, she digs up a spot in the pasture and carefully stirs it up to get the stuff just-so. Because it's fine particles, a fly sheet doesn't make much difference.
I just brush, brush, brush, curry, curry, curry, and alternately use a soft, damp sponge, dry cloth, and scrubby sponge to get her neat. Some days I say the heck with it and let her use her paddock and stall, most of the time I keep the paddock closed to let grass grow this summer. I pour apple cider vinegar into a soft sponge and work it into her legs, belly, and face to keep the flies from biting... she's thin skinned and hates them just crawling on her, though. Also always turn the fan on at noon.
Cowboy Magic and Showsheen is going to be your best friend.