Looking at making a nice design for some live rock and see that some people use cement, while most others use some kind of glue or other adhesive. What give the best appearance as your tank is in the earlier stages and you can see a lot of bare rock exposed? I'm thinking cement is more robust and will have the strongest hold, but glue may look better. Any thoughts on this? I'm looking to create an arch and a mini cave like structure within a 120gallon tank.