If you can find a good groomer that has the time and patience, they can work miracles and may not need to shave completely down. Although they charge a pretty penny for it. I have a slicker brush that I spray conditioner on and on the mat and can usually get even a bad mat out with that, but if it is all over, that is too much work. Even if he gets a shave, it'll be grown in before you know it. Don't feel bad about it, I think most of us have let our dog get matted atleast once. And now you have the perfect reason to get him a few warm clothes for the winter.