I have a pair of Costa 580g and they're phenomenal. The plastic version developed optical aberrations when left in a hot truck a few too many times. No such problem with the glass. As for keeping them on my head, I use Cablz Zipz. You've got to check where they attach to the glasses every once in awhile for wear, but I've not noticed any issues in over three years.
Oh, and my wife is director of research for the Flaum Eye Institute at the University of Rochester...does that get me "expert" points?