Replying to Grass Stain on ski

Here in wisconsin (or at least in the part I do,) we get barley any snow. when we do, i usually go to the local dump-turned into a ski hill. But this year, it hasn't been open. I just got new boots, so to break them in, i was just messing around in my backyard with my skis and all. since the 1/4 of an inch hardly covered the ground, grass was visible. I have some used old public enemys, and i have huge streaks of green (grass stains) all over the bottom and some on the topsheet. Do you guys know any thing that won't corrode the ski or mess up the wax on the bottom?
thanks