I'm currently building a tank with a waterfall in it. I used natural stale stone title from depot, that I broke up to give me different sizes. GE 100% black silicone to hold the titles together when I was stacking the waterfall. Great stuff pond and stone spray foam was used to give it over all shape. You can check out my thread I have of this build. http://www.frogforum.net/vivarium-te...exo-build.html