I've got the locking pin backs on the two pins I keep permanently on my camera strap. (The Donald motorcycle pin I use as my Avatar, and my Dis pin.) As previously stated, the biggest downside to these backings is their size. They stick out from the back of the strap a good 1/4".
I wear a special kind of shoe that has a setting screw in the heal. Whenever I take them to be adjusted, they put a drop of clear nail polish in to hold it in place. I would think a dab of this in the hole of a pinback would work about the same to lock it in place. It's clear, too, so it wouldn't be as messy (or permanent) as lock-tite.
Here's a tip for a more on-the-go fix if a pin is getting loose: I stopped at one of the pin stations during a recent trip and asked if they could trade me backings. I had one that was real loose, and I was afraid I was going to lose the pin. They didn't have a spare pin back to give me, although they did show me where they had packs of them for sale. Instead of buy those, though, they showed me a trick. For a rubber Mickey-shaped backing (as opposed to the metal ones), stick the pin through in a place other than the center hole, creating a new hole. It took a bit of force to get it through, but it was nice and snug when all was said and done.
Another tip: if I'm trading pins and the other person has metal backings, I'll ask them if I can keep my Mickey ones. They seem to hold better.