I use a similar system Patty. I tried different ways to pin my semps because things were aggressively moving the small ones.
I finally came up with a system of cutting plastic-coated metal wire hangers (so they won't rust and so metal won't be directly against the semp) into 4"-5" pieces, bending them into a sharp U, and pinning a few outside leaves down. So far only one pinned semp has been moved and that's because the mystery animal actually pulled the bracket out of the ground.
I would've liked to have seen the crazy strong animal (squirrel?) that did that...
