get a backdrop that has clouds or a sky and get a whack of angels, it would be fish heaven. or get a hellish backdrop and get a red devil. or do the piranha idea but instead of piranhas, get some buenos aires tetras or something of the like. you could also get a little hamster playground thingy and put it in the tank, fill the tank with water and add goldfish to the tank and hamsters to the play thing and watch the reactions you get from the little fish and rodents. man, i wish that my lfs would do this kind of thing. i'll keep thinking and posting. good luck!