^ this. I have a few hundred at this point and have yet to have any even try to chew the tubs, let alone actually get out. I just cut the pieces of left over 2x4 or 2x2's into chunks and toss them in the tubs with the rats. They gnaw on them and when the wood gets too nasty, I toss it and start over. It's worked great thus far, knock on wood, lol!