Forgot to mention that she never comes close to making them bleed though. I would definitely try to break that habit before it becomes ingrained, since he takes it to an extreme. Bitter tasting but safe substances on the feet may work, or Velcro dog booties which you can buy or make (check out...
I have a heeler who was adopted as an extremely anxious dog. She has since calmed down, but still nibbles her nails when she is either stressed or bored. It seems to be a nervous habit for her. She doesn't bite or lick her feet, but goes click click click on her nails...even her dew claws...