the excess foxes will end up as road kill. For supposedly clever animals, they have as much luck crossing the road as possums and coons, more than armadilloes, and less than chickens.
Hmmm...you sound like you speak from experience about fox roadkill. However, in the fox-inhabited places that I have lived (rural upstate NY for about 10 years) I can't remember seeing any fox roadkill among the groundhogs, raccoon, skunk, possum, turtle, deer, squirrel, etc.
I imagine it's a question of numbers--you must have many more fox in your area.