They are designed to stay down by being buried in the substrate which should fill the tray and then cover it deeper. The substrate holds it in place. The plants are not really great in tanks with higher flow, larger fish or many fish that dig. If you have no substrate, you have to get creative. Just gluing pebbles etc, inside the base is not enough. You need to attach it to something heavier or weight it with something like sinking driftwood,