As you’ve undoubtedly noticed, you and your dog have very different notions of what smells nice. To your dog, something could smell quite wonderful. But to you, in a word, it’s yucky. And vice versa.
A few theories
Here’s a perfect example of something that smells nice to you but not to your dog: the perfumes used in dog shampoo. You may find them pleasant, but many dogs dislike their odor. As a result, as soon as your just-bathed dog gets the chance, he finds something that smells more acceptable to him—garbage, dog feces, animal carcasses—and starts rolling around in it.
Have you ever caught your dog rolling around in poop? Believe it or not, this behavior is quite common—and very natural. Many believe it's instinctual behavior, harkening back to the days when your dog’s wild ancestors would mask their scent to help them sneak up on their prey. Wolves, for example, have been observed rolling in animal carcasses or the droppings of plant-eating animals, to cover up their own smell during the hunt.
Here’s a related theory that also conjures up the pre-domesticated past of canines: wild dogs may have rolled around in smelly things to “tell” their pack mates where they’ve been and what they’ve encountered in their adventures. It’s his way of saying, “Hey, smell where I’ve been!”
What should you do about this behavior?
The important thing to remember is that rolling around in smelly things is a natural and normal behavior for dogs—no matter how the results may strike you (or your nose). Of course, that doesn’t mean that you have to live with a smelly dog. Though you shouldn’t punish this behavior, there are steps you can take to discourage it.
If your dog rolls around in his own feces, immediately clean up after him in the yard. When you’re out walking your dog, keep him on a short leash to prevent him from rolling around in another dog's poop or other smelly things you both might encounter. To discourage and ultimately stop him from rolling around in offensively odorous things, you could try to pair an unpleasant experience with his action. This can take the form of squirting him with a water bottle or using a citronella spray collar that can be operated via remote control (dogs absolutely hate the smell of citronella). If you use this method, make sure you squirt him as soon as he starts rolling.
You can also try anything your dog finds annoying, like making a loud and sudden noise. The key here is to be consistent and to start the “annoyance” as soon as he starts to roll around in something smelly. Once he starts to associate rolling around in smelly things with the unpleasant experience, chances are this behavior will quickly stop. And you can breathe easier.