I can't speak as to being fog proof, but the Red Hot scope that came with my wife's Parker Tomahawk crossbow package is really nice.
It's got 3 separate circles to use as compensating aiming points, and if you get the IR version they light up either red or green at 3 different intesnities... I really like it
"When a hunter is in a tree stand with high moral values and with the proper hunting ethics and richer for the experience, that hunter is 20 feet closer to God." ~Fred Bear