I am a hay farmer (alfalfa) and we rotate our fields about every seven years. In the last few years, we are being overrun with rodents - gophers, mice, voles, and moles. The little rodents are ruining fields that are only a year old or two. We have tried different forms of poison, carbon monoxide, and propane/oxygen injection with explosion. All of these methods have been costly and we still have problems. The only time we seem to get rid of them is in a flood, but there hasn't been a flood for five years. Any suggestions?