I am having the strangest time trying to train Finnegan. He's just over 4 months and has done great except for carpets. He won't go on hardwood floors. We have a dog door and a fenced yard. He knows to go outside, but if there's a rug by the door he'll come back in and pee on it. So I have a choice, muddy floors or pee on rugs. I'm wondering if the rug feels like grass to him. Any ideas?