What is the hardest finish for old oak flooring. I have dogs in the house that tear up the finish, even with trimmed claws. After one year our polyurethane ( 3 coats ) looks scratched, but is not scratched all the way through to the wood. It looks like there is a separation between the wood and finish which can't be fixed with a recoat.

Knowing I will have to resand, is there any truth to the finish used on gymnasium floors being the hardest most durable finish available?