And if that doesn’t work you can pour hot tea on them. 
No hablo ingles.
Have you seen the opening of Everybody loves Raymond in the first season where Ray and Debra spot Ray’s family coming so they do there best to make it appear that noone is home by turning off the lights and the TV and hiding in a mad rush?
We did that a lot.
'im indoors got rid of the last lot of JWs by telling them that Christ was his third favourite fictional character after Batman and Porky Pig. Since then, nobody else has come knocking on our door…
I know a seminary student that invited them in to debate their views via the Greek translation of the bible. They lasted a little while & put him on the “do not visit” list.
The Mormons are MUCH better at debate than the JW’s, in my experience. I actually formed a rather sweet bantering relationship with a couple of the Mormon missionaries once who came to collect my soul, until they got yanked out of town (literally on 12 hours’ notice) to go somewhere else. You don’t think it was something I said, do you? 
Pepper Mill just invites them in and talks with them. There’s not a chance she’ll be converted, but she likes the company. If they really knew her religious views, I suspect they’d go running into the streets.
Or you could do what another grad student said he did – invite them in and watch as they react to the weird traps and events he pre-planned (like a painting done with wax colors that had a heater behind it, which he switch on before they came in) .
I love watching my mom talk to door-to-door missionaries. We’re Jewish and we have a mezuzah on our doorpost. She puts on her best primary-school-teacher voice and points to the mezuzah and starts to explain what it is, the history of mezuzahs, what’s inside, etc. When the missionaries start to look fatigued, she wraps it up with ‘and what you need to know is that this mezuzah means that my family has a religion and doesn’t need another’ and waves goodbye. The best part is that I think she really does want to educate them, so they don’t waste their time on the obviously Jewish houses.
The Jewish excuse doesn’t always work though. I had a man of some Christian faith come up to me in a parking lot here in Germany. When I told him I was Jewish, he got very angry and started yelling that I had killed Jesus. Eek.
I did my best to deconvert mine. When they mentioned Genesis, I asked them, “Which version of Genesis?” And I asked how they knew the Bible was the word of God. I was very nice, and pretty much just asked honest questions. The original lady came back with her husband, and he didn’t have answers either. Finally they stopped coming. Their parting shot was to give me a weak-ass anti-evolution tract full of dishonest quote mining. I was really looking forward to pointing out the falsehoods and ask why such seemingly nice people would want to disseminate lies, and posit that their church was making them look bad. But they never came back. I’m rather disappointed.
Which is why* I* don’t bug them * when they’re minding their* own business. If I went around to their house telling trying to give them copies of The Panda’s Thumb, they’d be perfectly entitled to slam their door in my face.
True story: a friend of mine was once approached in the subway by a JW or similar proselytizing type, with the following short exchange ensuing:
JW: “Have you accepted Jesus Christ as your Lord and Savior?”
My Friend: “Um, look, I’m not really --”
JW:“But you must! For He is the way to Eternal Life. Don’t you want to live forever?”
My Friend: (pause) (evil grin) “My Master has already promised me I will live forever.”
JW: backs away, then runs up the stairwell
My favorite response for a Jehovah’s Witness:
“I didn’t even see the accident.”
Mormon missionary transfers on short notice are not an uncommon thing at all, actually.
~OneCentStamp, former Mormon missionary
Why would you try to answer someone who, when you tell them you’re not interested in discussing something, demand “why not”? That sort of rude action deserves no response. Just close the door.
That’s the one - thanks!
It had me in tears - again.
I just tell them I’m not interested. Repeat once, say no thank you and wish them a pleasant evening while closing the door. Works every time and you don’t have to be nasty.
My favourites:
“Hi, you are trespassing on private property. Will I have to call the police?”
“No, thanks. We already have a God. And it is a real one”
If I have more time and I am in the right mood:
“Good, good, I am so glad you came. It is so hot out there, are you guys tired, thirsty, can I offer you something?. We have a new line of all natural energy drinks rich on antioxidants and vitamins. Let me show you. Here, have a brochure”. I actually have the brochure from some nutty pyramid scheme from a work mate of my wife. I make sure I stretch the pitch as long as I can without letting them say a single word.
Usually, “sorry, I’m not interested” works just fine.
I found that living in a rented room or an apartment has served me well. The front door is far from my dwelling.