I picked up these big lava rocks for my 29g aquarium. My girlfriend has me worried now if i put too many the aquarium might break. Is this really an issue? Also i suppose I have to worry about falling rocks. Anything I can do to secure them to each other that would be fish safe? I would like to give the fish some hiding spots and also create some height in the tank. I will have a lot of other questions on the forum but lets start here.