Welcome to FishLore!
I was going to suggest the fishing line too.
I've used it to tie java moss to driftwood and you can't see it at all once the moss starts to grow over it. I had an algae outbreak recently and ended up pulling the java moss off the driftwood. The moss had really grown into the wood. I've never had it tied to rocks. Maybe something porous like lava rock would work. In both a 10 and 20 gallon I have put a clump of java moss behind the intake on the
HOB filter and it looks good when it spreads out.
Good luck with your shrimp! Hope to see some pics.