Archosauria1

Hey guys, got a question. I’m designing a new enclosure and I’m using Great Stuff as a back wall for the cage. I’ve used the stuff before so I know how sticky it is. I want to insert rocks into it to simulate a decrepit wall(for a pair of wall lizards for my son). Question: Will Great Stuff hold those rocks in place? Or should I carve out a niche in the Great Stuff after it’s cured and use some construction adhesive to secure them? My concern is I don’t want any debris, feeders, mildew etc getting behind those rocks once the design is complete. I also want the enclosure to be as “maintenance free” as possible... I don’t want bacteria and mold building up in the dead spaces in the foam.