I was under the impression that a fox will lead you to the nearest undiscovered map location? I am 99% certain this has worked for me in the past. Scenes of it leading you to a cliff etc might be pathfinding glitches? Is there anything in the AI packages that hint to foxes leading you to undiscovered locations?
I wonder how many people tries this. It seems to me like you are treating this like real life so of course they would lead to nothing. If I was developer I would do something like this just to see the reaction.
It's like that coincidence theory, where if you pick words from the Bible in a certain sequence they "predict" WWI and WWII... it's just coincidence if a fox ever takes you to iron.