Rock Issue

I've gotten myself in a pickle. I've got my cichlid tank established with a stacked/caved flagstone setup but I never was smart enough to silicone them down. I noticed the rocks must have shifted overnight due to perpetual sand redecoration and so I need to fix this. What do you recommend? Stacking the rocks and bonding them when dry [outside of the tank] and putting the entire assembly in the tank once set? Is there any other way I'm not thinking of besides draining tank and starting over? It's a possibility but I don't want to stress the fish (and myself) if necessary.

If I'm not mistaken, there is a waterproof - fish safe - epoxy that set underwater.

Do a google search and see what you come up with.

DZ