An advert in a parish magazine is a good way to have a permanent advertising presence in the countryside.
It can be hard to find out what it is, but when you're in the sticks and you see a church, write down the vicars name and tel number if on there and give him a call. The name is usually on a sign or noticeboard.
I pay a tenner a year to advertise, although some charge more.
Not everyone gets a parish magazine, but the people who do are generally the community oriented types who get involved with village fetes or garden parties, fundraisers etc. And these are the type of people who have strong networks and are most likely to recommend you to a friend.