I would think it would fall off over time, since it is very heavy. Now I have thought about trying the mortar stuff to make something like that, but with wiremesh underneath. I am also looking to try epoxy. Almost bought some but I am going to wait.
they are at the thickest 1in and there not real stone there a kind of concreat mix there used for fire places and other kinds of rock decor and are compleatly flat on the back side. i used acuarium silicon and if that can hold a 30gal tank together im sure it can hold acouple stones. they feel preaty solid, but im going to let it run for a wile befor i add any frogs
Just be very careful. You might want to check what kind of concrete it is. Concrete will leech lime and can kill everything. Those that have a watergarden can not use certain concretes because of the lime. Like sometimes people will want to use concrete blocks in their ponds to lift plants up and that is a big no no.
You can do a search on Yahoo and just put in "Concrete Leech Lime", and you can read all about it.
For years I was a watergarden/Pond Master Gardner certified through PondScapes Magazine and the issue of concrete would always come up with new pond owners.
I wish you the best.