Remember the biggest problem with glueing or epoxying them together is that if you want to move them later you have a major problem, also, if they are all glued together how are you getting them out if you need to? I have seen people place their rock on pvc shelves, drilled and stacked on pvc pipes or as most people do, stacked together like a jigsaw so that they don't topple over and cause a rock slide and take out your tank