Doggie wiping his feet at the door...

It's actually fairly easy to teach that. You can also teach your dog to scratch a board with sandpaper on it (front and back legs separately) so they file their nails down that way. Someone I know did that, and forgot about the board and came home one day to find her dogs had scratched themselves to the quick and blood was everywhere. Oops. She put it away after that and only used it as needed.

Dogs, like cats, have an innate desire to sratch at things and dig, and that is why it helps in training.

my cat do it,not easy teach him but I did