Just keep on trying mate. The law of averages say you will hit lucky sometime. I am in the same situation myself. Farmers are a breed of their own and it helps if you are friends with them. Find out where they drink!!! I agree, you could be doing them a hugh favour clattering vermin. Some how, its hard to get through.
Another option.... From my experience is to get among the farmers daughters. The invites may come along in more ways than one. Haha..