That might be ok with the odd rat trying to move in but when you suddenly have a lot move in then its too big a job for a cat or cats. They are too busy shaggin and fighting each other. If one animal sees another as a food source they dont usually wipe them out cos there too busy eating one. Cats by habit dont kill numbers, like terriers do, and if a place is devoid of rats/mice the cats are redundant and so you have to feed them to keep them in which case they dont need to hunt rats and mice are easier for a bit of sport. Get terriers in I say and do the rats and then the cats!! good sport.