My dog runs on crushed blackrock in our driveway. There is no need to do that for him, as he runs all the time out there playing fetch, etc.

The rubber mats serve three main purposes. Easy on the feet, and digging prevention. They are also easier to clean than gravel. I am concerned about how hot the floor will get in the summer, but he will get some mid afternoon and late afternoon shade where he is. The roof will also help.