From the great idea file, comes PC Racing's Small Filterskins. Slip one over your dirt bike air filter where it will trap 90 percent of all dirt trying to enter your intake. (Your filter will easily get the rest.)
Between races or rides just remove the dirty Filterskin and slip on a fresh one. You're ready to go in a jiffy. They can be cleaned and re-oiled again and again. Sold in a package of three. This small size is for air filters from 5 to 6 inches in diameter and 2 to 5 inches long.