How about magnets if you want them to be moveable? That is how another product, magnaturals is made. One set of magnets is embedded in the foam, while the other set is used outside the aquarium. You can then move them around to any position you want at will. strong magnets will hold it firmly, but enable you to move it easily. I sell the Magnatural rock shelves and planters, but I am sure you could buy magnets somewhere and do the same thing.