Pour a box of Baking soda in the hole and the run, It kills rats, Rats are very clean animals and they get the B S on there feet and lick it off, and they can not fart or burp so that s what kills them , trust me it sure works and will not kill your chicken, and cheap to buy,
This isn't true, I've used baking soda for years in my pet rats cages and it doesn't harm them.