i would stick with as many larger pieces as possible, nothing more frustrating than trying to stack lots of small rock. zip ties, super glue gel, pvc framing, etc are all methods to assist in securing your rock work. take care that rocks don't fall onto the glass as they could scratch or even shatter the glass. also, its usually safer to put down some eggcrate on the bottom of the tank and put the rock on that surface, rather than placing the rock on the sand. all that being said, i second christina's recommendations. phenomenal has the best prices, although in my experiance aquarium designs usually has the nicest rock.