If you want them to stop coming, let them spend time with you, be nice to them. Eventually they give up. I know an X witness, they get extra "points" for dealing with the nasty ones.
I also have found that the ones who visited me lied about what they believed to soften my critism.
I have also found out some very, very hateful things about their behavior. The "shunning" they use is cruel and unforgiving. At least it has been in one circumstance I know of.