Roofus (also known as Roo) is the large dog belonging to Joe Stone. Although his sight is failing, he is apparently fairly intelligent for a dog and knows to bark to alert Joe to trouble during the night. He may well have been named for the sound of his bark, which is frequently rendered as "roof".
While Roofus is certainly a smart and well-trained dog, Joe credits him with more intelligence than he rightly possesses, due to her belief that she has seen him spell out a message for her in pebbles and rocks. The message was in fact left by Kokiro, whom Joe, like most Uians, cannot see.