We had a rat problem a few years ago and we tried everything to keep those buggers out of the milkhouse, feed, barn etc.... No luck. We even poured quickrete down their tunnels and THEY CHEWED THREW IT! The cats were afraid of them and those Rats would actually fight with our Dogs! They evaded every type of trap we used. We eventually had to resort to poisoning them. We made bait boxes out of various tins and old metal lunch boxes. ( To avoid them carrying the bait out and dropping it where the other animals could get it) We put rat size holes in them and placed the "cake" type of rat poison in them. It took about 2 weeks of continuous "baiting" but we erradicated them.