A promotional photo session featuring Ellen Barkin sporting a studded dog collar and attached to Jack Nicholson's leash had American feminist organizations in an uproar.
Other pairings considered were Diane Keaton and Jack Nicholson, then Robert De Niro and Jessica Lange, and then Al Pacino and Meryl Streep, before its final incarnation of Nicholson and Ellen Barkin.
When Duke's owner takes him back, he decides to give Harry another German Shepherd Dog, but it's clearly the same dog, its fur has the same color pattern. Even though Duke gets into the SUV and the "other dog" gets out in the same shot, there must have been someone inside who slipped a different collar on it (notice how the owner pauses for a couple of seconds before he lets the other dog out)