Foggy Goggles

I recently replaced my smoke-tinted AquaSeal Kaimans with a pair of mirrored ones, and all of a sudden, I can’t keep them clear for more than a few minutes. I never had the problem before with the tinted ones. My usual method (spitting on them) isn’t working, obviously, and I’ve heard mixed things about the “anti-fog” drops/sprays.

Anyone have another never-fail solution for keeping goggles clear?

And, as a side topic, has anyone else noticed that mirrored lenses are harder to keep clear than other lenses?