P.S. this is the small and rediculously expensive item that CGW mentioned. I check mine periodiucally to make sure that they are screwed in. They are, indeed, small and rediculously expensive... but the best option in my experience.
I also used those (eyeglass wearer).
I kept mine in place with a tiny drop of shellack/clear nail polish on the thread (the same I use for any other screws which need bocking).