Turtle
I used to have that same problem when riding in the rain or when skiing. I now have three sets of Smiths Goggles that have a tiny battery operated fan in them. These work great while skiing, making the fogging a thing of the past. During normal summer riding, I can use a regular set of Oakley goggles, but in the rain or cold fall riding I use the Smiths fan goggles. They arent cheap but worth every penny. If they fail to operate,send them back to Smiths, they will replace them for free, a great company to deal with.
John