Maybe the little dog is Lassie. You know, he will go home and bark and the Fool's mother will say, "What, Fool fell of the cliff AGAIN?! Okay, HONEY...GET THE ROPE!"
Seriously, I see the dog as a symbol of loyalty. Depending on the spread, question, and position, I have also felt that the dog represented a youthful sense of adventure. Don't ask me why, that is just what I felt.