Why did Ford never put a splash guard on the rear that covers the whole fender well. They just left it open on the front of the rear tires with a big gap right there for mud and everything else to get in.

 

Rangers used to come with them several years ago. They are the same as the rears. Buy another set at the dealer or use the ones you have as a pattern to make up a duplicate set from plastic or sheet metal. The holes for the push pins are already there.