This is kind of a little trick that i've done and will share.
depending the size of the area. sometimes if there is a wound or puncture or scratch where they went under a fence and the fur doesn't come back to cover after washing, you can cut it out and sew it up and you cant even tell it was there.
realize this is for spots like a silver dollar or so. i wouldn't try too much bigger or it would be noticable.
when you cut it out, you'll have to cut it in the shape of a football or you will end up with "puckers" but thats pretty common knowledge for sewing.
if its too big you are just SOL