How can I make my MacBook Pro screws stop screwing around? The title might be a bit misleading, but it's precise: the screws keep screwing out by themselves!

It's quite random and I'm not even sure how I've managed to never lose one so far. Most of the times it's the bottom ones who try to run away, some times are the side ones. The top ones, 3 of which are much bigger, never joined the dance and always stayed right where they belong.

What always happens is that I feel them getting out when handling the notebook and then I just screw them back with my nails until I get ahold of a screwdriver. What I wished to happen is they simply stay there, keeping the lid in its place as they were meant to be and quit acting up on me!

Anticipating some comments:


The screws look all right and fine to the point that doesn't make me think I'd need replacements. This is a behavior I expect more people have with their MBPs so I'm also looking for shared experiences (the photo shows the same MBP model, by the way) here. And then again, maybe all I need is replacing them. But do I?
There are no Genius bars here in Brazil and I'm not willing to go on apple stores searching for something Apple probably doesn't care about &lt;-- I'm looking for practical solutions like the one accepted there. And trying to understand what could be causing this weird issue.
The first time you unscrew the screws on your computer, you'll notice there's some blue gunk around the threads.  That's Loctite.  It's essentially a sort of superglue for screws to help them stay in.  The glue adheres the threads to the casing, but isn't strong enough that a decent screwdriver and some wrist action can't break it.  I'd probably recommend finding an appropriate bottle of Loctite and then dabbing a bit on the screws and then screwing them back it.  That should keep the suckers from comin' back out. :)  I'm not sure about prices in Brazil, but in the US a bottle of Loctite (or something similar) should only cost you a few dollars.