There's lots of ways to kill rats - however more will always find their way to you unless you prevent them from doing so. Make sure your home has no opening into the house that are easy to get into and make all food hard to get to. Put pet food in plastic tubs, human food in glass jars and cans, and avoid buying anything in a box unless you're willing to put it in another container. If you don't have pets also make sure there's no water around - no leaky faucets or anything of the sort. Finally things like moth balls may make it unpleasant to explore new areas. Basically you want to make it difficult to impossible for them to live and thrive. Once they figure this out they won't come around any more and you might be able to be a little more lax. Also consider adopting a good hunting cat - one who is a proven rat and mouse killer (as a lot of cats these days don't hunt anything besides feathers on strings!) A good cat can do wonders.