Flagging, not calling, may be the answer in the fog.
"On calm, foggy days a lot of guys want to get really excited on their goose calls and make a lot of noise. Often, I do just the opposite. When it's foggy, listen closely and try using a flag instead of a call when you first hear geese, not necessarily when you first see them. This can be particularly effective when you know that the geese are close and they're coming toward your spread. I owe a lot of my success in foggy conditions to this technique. Try it, and I guarantee that you'll agree."
—Tim Grounds, Johnston City, Illinois