well you could get a chemical like disappearing ink, fill a super soaker with it and coat them and the snow, something that is clear now but will change color later, or better something that stinks reall bad later, im sure there are chemists in you college that would do it for a favor, thats just an idea, also coat an area of the snow with said chem's so if people mess with it later it gets them, but then avoid the area so you dont get inked