Alternator Dust and Belt squeaks. How to fix them.

Hello all,
   Over the course of 4 years owning my pride and joy, a Toyota MR2 MK1(although I hear the MK2's have this issue), I've replaced the belt that goes around the alternator pulley, 4 times.  Each time it has fixed the problem but it's annoying when everything is running so well and then with just a bit of dust and some rain(thanks to the vent being right over the top of the alternator and belt assembly, there it is again, that dreaded canary under the hood twerping away.
 
I was just curious to know if anyone has had a good method of removing this pesky problem once and for all or is belt replacement the simplest way(my reasons for changing the belt are that it normally goes 6 months without an issue but around the 8 to 9 month period, squeaking comes back.  Sure you can simply re-tension the assembly but I've found that once a belt shows any sign of stretch etc, it's been much better to simply replace it(they don't cost a lot) rather than adjusting back and fourth.  To me, belt slip(normally the cause of the squeaks) equals worn out belt, which unlike other cars with direct exposure to sunlight, rain and dust is going to wear.  By rights I always recommend to people when there replacing there timing belt, to replace all drive belts as well, since they too will eventually wear out, not long after a timing belt is due for replacement and that way you drive along with the peace of mind that a belt is going to go on you at any moment.
 
Please do share if anyone knows of a better solution.
 
Thanks,
Sean.