I agree with the previous replies: fiberglass can end up looking like
the wood, though the scratches >may< not be as drastic. Even metal
doors can be grooved if the dog is big.
I like the idea of kick plates. My first thought when I saw magnetic
kickplates is that the dog may be able to move them or pull them off,
but I have no knowledge of such a thing happening. Of course, if you
use magnetic kickplates you'll have to buy a steel door.