How to prevent plagiarism of my papers?
You've handled the conference plagiarism very well.

But then you say you've stopped putting your papers on your website: and I'm afraid that that is completely counter-productive.

It would be far more helpful for editors, reviewers and publishers to have your papers on your website, indexed by all the usual search bots, and clearly copyrighted and time-stamped. That makes it easier for them to spot duplicate content, early on.

The point of publishing your work is to get it disseminated. Very many journals allow authors to host preprints or similar on their own university web pages: do so. Get your stuff circulated as widely as possible. That gives you the best chance of other plagiarism of your work being spotted early on, in the future.