I like the flat you used, Lynn - I have a few precious ones like that; great minds think alike, I was going to use them for my Sedum wall! Could you just string some wire or even fishing line across the top in a couple of places instead of taking it all apart and putting netting on it? That would hold it in place. Once the plants root, I think they will stay in by themselves if you just have four strings/wires/fishing line to hold the rockwool.
Just a thought...
