Don't tell anyone but I used a heavy duty wall stapler and some 6mm staples last weekend on my redmoor.
I wouldn't worry about the rhizomes being damages anyway. As long as the roots attach to the wood/rock then the rhixome can split etc. The plant will find a way to grow. Much like a tree's bark will shape around any 'belt supprts' that are strapped around it.
I usually use cotton thread or elastic bands but got a little peed off by the amount of time this takes. The staples will probably rust but not enough to colour the water or add a high amount of anything to alter the tank params or cause trouble.