However I have managed to edge all the caverns with a mixture of sand and wood glue, which |I love as it sets "rock" hard. Its like making concrete on a small scale. Very strong. I even decorated part of my garden wall with a pattern of the stuff, not expecting it to last even a few storms, but miraculously its still there!!!
So I use my PVA concrete on most of the terrain models I make.
The only problem is that I always make either far too much or not enough. Now not enough is not actually a problem, just a bit annoying, but making too much sends me scurrying, yes I can still scurry, for other projects that I need the PVAconcrete for, not good planning.