thats not a bad idea either, really big gravel... "rocks" lol. food falling through the cracks could pose a problem so what you could do is have a feeding area, like a bowl or something where you always put the food. a bowl sounds kinda ugly though so what you could do is take some larger pieces of slate and use aquarium silicone to glue them together to form a "bowl" that looks natural. you could even think of it as a roman amphitheater where the little chopped earthworms go to do battle with the big bad bichirs lol. you know, something that might strike your imagination. have fun with it.