Need help epoxing my rock work.

[Dwb5]

I have had a large shelf glued for about a year now in my tank. The other day I was putting after frag on and it came loose. I have tried to epoxy it back on with no luck. Does anybody have any ides on have to get this to stay and not every worry about it again? Here is a pic of what it did look like. Sorry if u have to zoom in on it.

 

[KorL]

Kind of tough to do underwater. Maybe epoxy mixed with super glue and have something supporting the structure while the epoxy cures