You could make agrocrete rock covering the PVC parts. (sand cast the rock with the PVC inside of it, use paper towels and masking tape to keep the mating surfaces clean).
You could also use black silicone to cover the PVC and stick rubble into the silicone as it sets up.
Otherwise, yea, HD for cheap superglue. Also I saw a whole bunch of gel in one of those dollar stores the other day. IIRC it was like 4 tubes for $1