Ok for those interested, having used some man made pebbles they don't stick well to the aqua kneed. What I have been doing is going through the toppled frags as they happen and remove this plastic pebble and stick the frag back on the original spot.
My frag plugs were stuck down using aquakneed and gel super glue but they keep coming free on the pebble aquakneed connection.
Aqua kneed on its own does not stick well to wet rock so I put a drop or two of superglue down on the aqua kneed and it sticks heaps better when it all sets hard.