Mothballs work as a deterrent.......Put them under your Coop....Make sure pets can not get them.....
Cheers!
Sorry, but I don't think mothballs would have a great effect. If there wasn't already a nest under there, maybe. But it's not like moth balls are a rat's kryptonite. They basically just smell bad. I think the rats would just push them back out the tunnels. Or learn to live with the smell.