It's very, very simple. There is one 100% reliable solution to the scunthorpe problem, and sooner or later, it's the one everyone settles on. Don't filter in ways that are vulnerable to the scunthorpe problem. Just don't do it.
For example, if "ABC" is a bad word you want to prohibit, prohibit "ABC", not "AABC", not "ABCC", but "ABC".
But even then, you probably still shouldn't do it. Blocking on the word "porn" will block scientific articles on the effect of exposure to pornography. Blocking on the word "bitch" will block articles on breeding dogs. Filtering based on keywords is just not particularly good.