alright--just b/c i should be setting a better example: duckie suggests that anything that will keep your rope from being directly on the dirt is a good start. old blue tarp, shower curtain, tyvek house wrap, epic fabric, old garbage bag, wrapper from a mondo burrito, etc.
some materials probably keep dirt from getting to the rope from the bottom better than others but i doubt it makes that much difference. hell despite my best efforts my ropes always come home at least a little dirtier than when they left.
*i want the bunnies back but being duckie is special too*