I've had my share of discussions with JWs, dating back to 2010. I was polite with them, but utterly unwilling to give any ground to them and indeed, had answers to their questions that I don't think they expected. After 2012, they quit coming, though, I suspect because they realized they were out of their weight class. I think that politeness is important, too, because it takes any opportunity to complain out of their quiver, and considering atheists are still considered the least trustworthy of any major societal group in the US, how we conduct ourselves is no small matter.
Still, if you've had your fill of their intrusions, I have no problem with your approach.
A couple of years ago Dr. Kellie kept us abreast of another strategy for discouraging door-to-door proselytizers in "What Boobs are Good For".
LOVE the shirt - wish I had the guts to wear it!
There's others, Elizabeth ... lots and Lots and LOTS of other T-shirts to choose from! Trust me! [BIG grin!]
I like that. My last visit from them was 2 years ago and I told them to give me a minute to get the holy book, I came back with the Gospel of The Flying Spaghetti Monster and they tried to hand me some of their things while quickly departing.
I don't mind much when the JWs visit. I'd rather they didn't, but am willing to talk with them when they do. My favorites of their "conversation" starters are, "Surely you know that Jesus Christ was the one perfect man" and, "The Bible is the unassailable word of God". There's a lot to work with there. Typically, they'll stop by every other Saturday for a year or so, then give up until someone new who doesn't know me takes over and sends them again. Because I'm always polite and only mildly challenging sometimes the elders bring adolescent acolytes. I imagine them briefing their young charges on meeting a real, live atheist who just might be ripe for conversion. That's when I become more challenging -- asking the young ones whether they can really believe what their preacher is pushing. Sometimes I see wide eyes of comprehension, and that's my reward for months of intrusion. Then they stay away for a year or so.