As both a longtime (lifelong!) fan of Peanuts, and as a lifelong lover of dogs, this is my all time favorite strip. I once had a dog that, when he got tired of the fetch game, would pee on the object being thrown and walk away. I sometimes wonder if Schulz had a similar experience, but cleaned it up a little for this strip!
I think he was showing the angst of his early years, dealing with the giants we called grownups!