OK. Get a piece of cardboard and a magic marker. Write on it:
"NO SOLICITORS"
Fasten it to your door.
That doesn't work because what they are doing is not technically soliciting. Soliciitng involves selling something. They are not selling anything nor are they asking for donations. If you ask them to leave and not come back and not leave their pamphlets, then they usually wont come back for at least a year.
I used to kick them out all the time, but one time I actually engaged them and found that they weren't so bad. I actually found it enjoyable to talk with them so they kept coming for a number of weeks. But once I told them I was done, they stopped coming.
But really, if you are like me and enjoy discussing religion, then engage them. They know the bible like no other Xtian you will ever meet.
Ultimately my conclusion was that they weren't any more fanatical than any other Xtians.