Here is a way that will keep them from coming back to your door.
Next time the JWs come to your door, bring out a copy of Ray Franz's "Crisis of Conscience" book and start asking questions about it and from it!
After "sharing" this book with a few of their visits, they will "mark" your house as a "do not call" and will not return.
The JWs cannot stand Ray's CoC book
--VM44