Discussions

First I am not starting this message to start any fights about religions or anything like that.  
 
I have had a few JW's come to my door today. I answered the door once the 2nd time I did get the door in time before they left. My question is how do you tell these people that you are not interested, cause I know they will try and try and try. I really don't want to slam the door in their face or anything but how can I tell them nicely. I am not religious and I know if say that to them they will stand there and preach to me.  
 
Also I have to open my door to see who is there cause I don't have a peep hole and if I look out my window, well they will be able to see me.  
 
So any suggestions on how to handle this nicely, and I am talking about any religious people that come to the door.