Politely introducing yourself and asking is what usually works best. I have had luck by offering to help out on the farm or performing some other service for the land owner. My buddy is a diesel mechanic and I'm an HVAC tech so between the two of us there is usually some service the farmer can find for us. When you save him a chunk of change by tuning up his tractor or fixing his freezers there is a lot more appreciation. Be prepared to hear a lot of NO's, just politely thank him for his time and take your leave.