I'm actually having the same problem. I pretty much stopped abruptly about a year ago. Now there isn't a weekend that goes by that I don't get a visit from an elder or a pamphlet in my door. It's really irritating. One elder actually asked us if we would go out to dinner with him and his wife. I told him no. The last time he came around my house, he started to berate us in front of his wife, who is the biggest gossip. I don't think I feel like subjecting myself to such verbal spankings.
I tried the whole "I don't feel like going right now", "I'm fine and have no need for visits", ect. It didn't deter them. If anything, it solidified their assumptions that I need saving. If you figure out a way to get rid of them for good, let me know! That stuff is worth money!