I live on a farm, at the end of a barely-paved road, with the nearest house nearly a mile away... AND WE STILL GET THEM! What's worse, is that in addition to the Jehovah's Witnesses, the Mormon missionaries, and the politicians who come for signatures to drum up support, and the magazine salesmen, we also get FARM SALES REPS! We grow avocados and Satsuma oranges, so we get every kind of fertilizer and pesticide salesman, and farmland leasing and harvesting agencies wanting to sign us up, and all kinds of crap.
I have learned to just say "NO" politely and firmly, and to repeat it as many times as needed while still being polite. If you start to lose your cool, they will use that to try to get you to buy something just to get rid of them. A sale is a sale to them, even if they have to leave with you hating them. For the politicians, I flash my Texas license, and say "Sorry, I'm house sitting, and nobody will be here, who lives here, for the rest of the year (or until after whatever election has happened). That gets rid of that one, plus no more from the same party should bother to come later.
And most importantly: Place signs in plain sight, and in alternate languages if you live in a multi-language community.
"NO SOLICITING" and "NO PEDDLING" and "NO PROSELYTING"
Charles