I have been trying to anchor some moss to a rock for some time and it keeps coming loose one way or the other. Tying it down will not work now because that would involve removing the rock which would upset too much (it is a big rock). Gravel lasts only a few days before something knocks it off.
So I bent up a couple of larger paper clips and these might actually weigh down the moss in one place for 2-3 weeks - long enough that I could then remove the clips. Any problem with that?

So I bent up a couple of larger paper clips and these might actually weigh down the moss in one place for 2-3 weeks - long enough that I could then remove the clips. Any problem with that?