the substrate is caribsea floramax, which i have never used before. right now the hills are staying put on their own, however, i suspect i am gonna have to add some plastic retaining wall type reinforcements before i add water. the "cliff" in the front area of the right side appears slightly more sheer in the photo than it is in reality. i am hoping i will be able to retain that shape when i plant/flood the tank. gonna take some figuring i reckon.