Also think about what is going in your tank will the inhabitants be digging under the rock or trying to bulldoze it? We have an orange spotted goby that love to topple our rockwork in our 29g and a urchin that trys to knock rockwork over. If you find a way that you like you can drill small holes in the rock and zip-tie them together so they won't fall and can still be removed if need be, unlike glue/epoxy that are permanent. The zip-ties become covered by coraline very quickly so you dont notice them.