I know when I was setting up my tank someone told me to use aquamend to hold the frags in place I don't see why it wouldn't work for LR too. I found it only at home depot. Coraline algae will grow over it too. Holdfast is the same thing and can be gotten at the LFS. I didn't have to use it for my rocks so I pasted it on to a friend.
https://www.marinedepot.com/Aquariu...Aquariums-Instant_Ocean-AS4711-FIMTEP-vi.html
https://www.marinedepot.com/Aquariu...Aquariums-Instant_Ocean-AS4711-FIMTEP-vi.html