If I am getting this right.... you want to have a real false bottom, then have the cave drain into that and then pump back up to the back of the cave so the view would be water coming out towards you but not accessible to the frogs.

substrate ------------------------
------------------------ _____________ Egg Crate 2
--------------- --------I
_____________ I_____________Egg Crate 1
___________________________Bottom

Egg crate 1 to be complete bottom but cut away at end of water run
Egg crate 2 to come to front to separate land from cave

Egg Carte 1 to be topped inside cave with what water will flow over but stop before glass to allow smooth runoff.
You will have to have an area to access pump from behind so look at Mikes construction journal for how he made his access to pump and the hose can come up the same hole.

Are we on the right track? Hope this is planting some ideas or helping finish off some ideas you have.