I leave a bowl of vanilla bean scented ash/sand in their cages at all times for my two babies and for my solo degu. As I read through the different posts, most people give the sand occasionally. It does not cause harm to leave it in their cages, does it? The bowls are deep and they do not make a mess. The critters love jumping in and out even if they aren't playing in the sand itself. The aroma from the vanilla bean scent is wonderful!! I can tell when the critters are playing in it because the room fills with this great aroma. Aside from having to remove their excrements, I like to leave sand in their cages.