Hiya, go to a farm shop if you have one in your area and buy "Neosorexa" put loads of the stuff down under your shed, don't worry about the cats, it will not affect them, modern poisons have no secondary affect. just put the poison in plastic bags and get the bags well under the she, the rats will soon open the bags. If you cant get Neosorexa, try and get one of the products containing difenacoum. The most important thing is to ensure you are not tight with it, put plenty down or the rats will become bait shy. Good luck