I build all of my rocks like that. It is practically free and kind of fun.
All of my rockwors is off the gravel on pedistals of this "rock"
Here is a piece under construction and the algae covered finished piece.


Can you tell which are the home made rocks? I can't, as some of them are many years old.

I know that green "S" shaped piece toward the right and top of the tank is the same piece in the picture I posted above



Here is a close up of that bottle in the center of the picture on the bottom, also home made.

Looks like Columbus dropped it off his ship, doesn't it? It is not that old