After building my raised beds and planting my tomatoes and other veggies about 3 days later I get these big mounds of dirt around the outside of the beds. Thank goodness I put hardware cloth at the bottom of the beds. Anyway, I've tried gopher bait with no luck and then tried flooding the tunnels today but have no idea if that worked yet. I was thinking about backing my tractor up to the beds and giving them a good dose of carbon monoxide but wondered if the fumes would leach up through the soil to my plants and hurt them if the tunnels are actually under the beds. Any advise?