Now accepting suggestions for making fake mounds of ground to place on a flat concrete floor. Can't drill into the concrete and don't want to haul in buckets of dirt. What I'm looking to do is make a mound big enough to set a couple of resin toads on along with some fake grasses and cat-tails. I'm wanting to make several of these mounds. They don't have to to support the weight of a person, but I don't want them to blow away either. I've received a suggestion of using sand to make a mound. While tthat would probably work, I don't want to have to clean it up. Any ideas?