Jenene,
I used the 2 part stick epoxy and assemble the rocks dry and let it cure. I used instant ocean holdfast and the color blends well with the reef saver rock but if you look on BRS they sell different kinds. I picked up mine at petco in the SW section. I thought about getting BRS's extra thick clear super glue but I didn't. The way I bonded mine is I put some epoxy on the contact surfaces on the bottoms and then filled the seam then I stuck the little pieces of rock on to the seam to make it blend better. I did some crazy rock work and it all has held together very well.