I used to run them off by explaining that I’m an atheist. Usually they would turn pale, start stammering, and run as if Satan himself were on their heels. Mind you, this works best in the South, where everyone thinks atheists kill infants at the full moon. I doubt that it would work here in Philadelphia.
Usually I just answer the door innovatively.
If the offending individual is male, I answer the door armed with a broadsword. Most of them flee immediately. I started this practice after an overzealous salesman tried to invite himself in for dinner and “entertainment.” I’m afraid I had to whack him a couple of times…
For females, or group efforts, an effective shoo-off is coming to the door stark naked and saying, “I’m sorry, could you wait just a minute while I finish casting the magic circle?”
If you really want to disturb them, show up naked and carrying the sex toy of your choice. (Although this may also disturb your children…)
One of my guy friends insists that the best way to run off door-to-door people is to answer the door in your skivvies, armed with a liter bottle of vodka and a wad of chewing tobacco. He says it helps if you spit frequently, just a little off to the side of the missionary’s shoes.
If you want to proselytize back at them, check out the Freedom From Religion Foundation www.ffrf.org. They have some nice little “non-tracts” to annoy missionaries with. They’re pretty cheap, and you can get a variety pack. Fairly mild-mannered fun.