I think it became an exercise in pushing shapes in slightly recognisable ways, looking for unique ‘characters’.
And one of these characters happened to be Derek. He’s at the bottom right of the sketches below. Big nose, ‘tin tin’ hairline, floppy ears.
He eventually morphed into a more ‘adult’ dog character. More of a ‘runner’ type dog. But still with a large appetite, and belly to match.