Fog is created from moisture in the air. With full seal goggles, you begin to sweat creating moisture, the heat from your head causes that moisture to evaporate, the goggles seal in that moisture and as it hits the cooler plastic of the goggles it condenses and creates a thin layer of beaded moisture that we call fog. If you sweat a lot, or if your head gets quite warm you will ALWAYS have fogging issues. No set of goggles will fix this. There are a few goggle systems that have a fan in them to help alleviate the problem by changing the air out inside the goggles and help cool off your face. However these systems are pretty pricy and run on batteries, so you have to have a battery pack attache to your goggles. You also have to make sure you're changing out the batteries regularly epically with how often you have to run them while on the airsoft field to keep from fogging. Although anit-fog wipes work for a while. There have been times when I have gone through 3 wipes in one day (and that's multiple uses with each wipe) because I have serious fogging issues.
I have heard good things about this stuff
https://www.google.com/search?q=Cat+Crap+Anti-Fog&hl=en&source=univ&tbm=shop&tbo=u&sa=X&ei=Wqc_UbbbKJOrqQHroYCABg&ved=0CFwQsxg&biw=1152&bih=679 but have never personally used it.
The way I run is with an pair of ESS low profile goggles, and an extra pair of shooter glasses. When my goggles fog, I slip into the shooter glasses for a bit and then back into your goggles once they have cooled off. If your running indoor events where goggles are required, I'd suggest wearing them when in combat and between rounds slip into the shooter glasses. But remember the longer the goggles are warm (around your head or neck) the cooler the plastic will be compared to the inside of the goggles and the more fogging issues you will have.
A quick EBAirsoft search also came up with these...
http://www.ebairsoft.com/power-airsoft-goggles-black-p-2795.html