How about putting a pro on the job, certain dog breeds will hunt them and take care of the problem. They are doing what they love and "nature" is taking its course. We had a scrappy little rescue dog , Lemmy , who found his purpose in locating these critters. Much to our surprise, and disgust, one day while we were out back in the yard. He quickly found one, before we realized what he was doing, and disposed of it.