Hi,
I had lost three, too. I lost one when I made the mistake of letting a WalMart rotate my tires during a road trip. I noticed the wheel cover wasn't secured properly. Upon inspection, I saw that one of the retaining clips was broken. I put the cover on as best I could. But it flung off somewhere in the desert. The covers were $62 in 1999. WalMart bought that one. The next one likely came off while crossing a cattle guard at high speed. I lost the next one in a pothole in Oakland. After replacing nearly a set
(BTW, they can be had for $36 at Impex), I decided to remove the wheel covers until I moved out of my pothole-ridden area. I painted my steelies gloss-black and ran ghetto-style for 18-mos:
Within months of moving to VA, I lucked out and landed a set of VW alloys. Now I don't worry about losing wheel covers, although I still have a full set for my "winter wheels." FWIW, I won't another car without alloys. /images/graemlins/smile.gif
But to answer your question, I made it a point to check the alignment of the wheel covers from time to time. I ensured the openings in the covers were centered over the openings on the wheels. I think after hitting a pothole or two they shift off center, then ride up on the valve stem and pry themselves off. But that's just my theory.
Good Luck,
Scott