A Dog's Three-Dimensional World of Light, Shapes, and Scent — Mostly Scent?

Is Marco the dog following a visual trail, with the additional visual cues of rocks lined up on the side, or is he following "a rippling, three-dimensional tapestry of light, shapes, and scents, with every object effusing odors that are further revealed upon nose-first investigation"?

According to the researchers interviewed for this article in Popular Science, "Why Your Dog Needs to Smell the World," too many dog owners neglect smelling opportunities in favor of motion. 

Many dogs, however, live in less enriching circumstances. They spend most of their time in relatively scent-impoverished indoor environments and then, when taken outside for a walk, are hurried along at a pace that’s more about their caregiver’s interests than their own. Even just a cracked-open window can make a difference, says Horowitz, though she tries to let her own companions, Quiddity and Tilde, sniff to their hearts’ content while exploring on a stroll.

Dogs change too: Our former collie-mix, Shelby, used to charge forward on walks. She never learned not to pull the leash -- or I was unwilling to correct her again and again times 1,000. 

More often she was off-leash except for the last bit of the walk home, past the other houses.

But as she aged, she more and more prefered to take "sniff walks," going a couple of yards and then pausing to examine some tuft of grass or bush. That is what old dogs often want to do.