So I was helping a friend make some rock structures and decided to make a little thread going over the process. We used Hydraulic cement, purchased at Home Depot, and that was it. Originally he wanted to drill holes and cement rods into place. Once he saw the strength of the bond, he opted to just cement everything into place. Pros=easy, cheap, super strong, won't crumble rock from drilling, reef safe cons=don't get to buy tons of 2 part epoxy, cant buy acrylic or fiberglass rods, can't use a drill Equipment=Hydraulic cement, water, mixing stick, and container First thing you have to do is mix your cement. It cures quickly, so only mix what you can use in 5 minutes. You want to follow the mixing directions, but the end product is thick, and almost stands on its own. If you want to use rods, I suggest going to Home Depot and getting these driveway markers. They are made of fiberglass, and you can cut to size using a hacksaw. Drill your holes with a 3/8 mason bit. Your rocks should already be fitted in the way you want them. I will use other rocks, boards, whatever it takes to hold my rocks into place. Then you take a liberal amount of cement, and apply at the joint, and all around it. Dont worry, you can either leave it like it is, or spread some sand over each joint. Coralline will cover it eventually, and it also makes a good spot to epoxy encrusting montiporas on. Once you get all your rocks cemented, wait an hour or two, and it should be fully cured, and very strong. This is best done with dead rock, some people soak their rock in RO/DI for a week, I never have. Now your four rocks lift as one, super strong and won't crumble. Later I'll get a pic of how strong it is.