Sometimes they dig to dull their claws, otherwise it's instinct. Over time if when in the act you catch them and 'punish' them, not severly, and not with hitting or negative reenforcement, just how the mother would do it then pup will stop.. you always still have to pay attention and make like an 'uhuhuhhh.. I don't think sooo' noise and they'll connect that with 'I shouldn't do what I'm about to do'..
