>Once I knew a guy who kept such people out of his house by pretending to film gay porn. It always worked.

That's sounds a bit unnecessary.

I always just invite them in for a chat, or I might take their literature and say "Sorry, I'm not interested in talking now, but I suppose I may have a look at these pamphlets, thanks", and they say "Ok, well here you go! Have a nice day!", and leave.

No reason to be rude. Unless they're being offensive, which is something I've never had to endure from any Jehovah's Witnesses or the like. They've always been quite sweet to me.