Corky and our Devon Rex cat have got along well for the two months the dog has been here. Recently, however, Corky has started resource guarding his crate with the cat. We thought the issue was food -- his rescue group trained him to eat in the crate -- and have been picking up Corky's food dish about 15 minutes after we put it down. I'm realizing now, though, that Corky is guarding his crate, not just the food. The cat has, in the past, slept in Corky's crate when he's not in it. The cat likes boxes. Corky now won't let the cat in his crate. He sits in it or by the door and growls. If we close the door he sits next to it. If the cat even walks by the crate, Corky growls or sits and stares with his ears pulled back. He's never lashed out and we quickly tell him "NO!" whenever he starts. Should we worry that Corky might hurt the cat?