You can put anything you want on the back wheels, but the fronts are factory installed from Ford. If you look you can see they are connected with 3 push pins to the inside fender liner and hang down maybe 2 inches. Check both sides to make sure you don't have one or both missing.
While I suppose you could modify a flap and attach it to these to get more coverage, I haven't tried. I do know that aftermarket ones will interfere with the running board as I bought some and had to return them.
I can look if you need to find the part number as it was a real pain trying to find it when I was missing one. Ford has a weird name for it and as I recall you need to look at a parts diagram for the running board, not the fender or body.
