It would be *really* cool if a small monkey was trained to ride the dog.

The monkey could be trained to memorize a list of commands. The owner of the monkey-dog-cart system could give him the list before they set out for their journey.

The monkey could whisper in the dogs ear, "Okay. You're going to want to make a left up here after the pond." Or he could tickle the dog in a predetermined way which would be equivalent to the oral directions.

When the dog did as the monkey ordered, the monkey could be trained to give the dog a Cheerio.