I got a clear "eye protector" thing from Home Depot, because it seemed like it would protect my eyes from the rain, and it does. The problem is that fog can quickly build up on the inside. What can I do to prevent this? Drill holes? Where would be the best places to put the holes? Would it defeat the purpose of rain protection? Should I just trash it and get something designed for the purpose (is there anything?)?

smear the inside with a very small amount of washing up liquid, then rub it in with a lint free cloth.

I have had luck with this trick. Apply FOG-X to the inside frame and RAIN-X to the outside of the frame. May have to re-apply once in a while. You might want to try them on a cheap pair of glasses or eye protectors first to see if you like how it works. I also use FOG-X on my bathroom mirror!! GOODLUCK!

I've used a thin film of hand soap successfully on motorcycle helmet face shields. Lather, apply, buff. Keep it mild. I love Lava, but you want to stay away from anything gritty in this application. I've got a friend who swears by shaving cream applied and buffed in the same manner