That's gonna be tough.Anything you put down will get dirty from wind,animals,ect.If its loose ,it will blow away.Anything solid might kill the lawn or plantings underneath.If it were on a patio or driveway,you could paint plastic sheeting then sprinkle plastic snow on it while it was still wet.But you would have too redo it,once it wore off.Hmmmmm,I'll have to keep thinking on this one.