I did this with my top jaw. I used what I think i remember to be a piece of redwood fence post from Lowe's or home depot. It worked well because it's relatively soft but not so soft that the anchoring screw would end up stripping. With it being a little softer, I was able to get the top of the top jaw imprinted into the surface of the wood a bit which helped prevent it from wanting to walk around.
I did three-ish rows, alternating the direction in each row. One away from the screw, one towards the screw, etc. it works very well.