Possibly for the same reason we do although we can argue what constitutes a nice smell.  

Dogs love rolling in stuff we don’t like the smell of. Some dogs love this more than others but most dogs, if they get the chance, will drop their shoulder and smear themselves with rotting fish, fox scat or cow pats. Owners generally find this behaviour disgusting and will try to stop their dogs by using a whole array of training methods. When they inevitably fail the dog will end up in the bath covered in what we humans think is a much nicer scent. Then once the dog has been pampered and dried off it goes to find something it finds more pleasant to roll around in. 

So why do they do this?

There are a number of theories, which try and explain this. The most popular being olfactory camouflage. This is where an animal covers itself with the smell of its intended prey or its own predator to disguise itself from being seen or eaten. The California ground squirrel, for instance, chews up and spits out rattlesnake skin, then applies the paste to its tail. The rattlesnake, which senses by smell and body heat, is confused and hesitant about attacking another venomous snake. So, do dogs camouflage themselves? Do they purposefully seek out their intended victims scent and cover themselves in it before they hunt? Observation on wolf hunting behaviour suggests that perhaps this may not be the case. They simply don’t roll in something; they are hunting and then go and hunt it. And there is no evidence to suggest that they roll in their predators (human) scent either. So, what other reasons might there be?

They maybe self-medicating and trying to get rid of external parasites. It is believed that horses roll in mud to ward off biting insects, to cool down and as a sun block. This may partly be the case in dogs but why such awful smelly substances and not just grass and mud?

A more interesting theory is that perhaps carrying home scent to your group members might serve to proffer important information about the surrounding environment and maybe even your hunting prowess. When a dog or wolf comes back from being away from the group and is covered with scent, other group members are intensely interested and crowd around sniffing intently. The dog seems to proudly shows off how well it smells and perhaps gains social advantages from being such a clever dog.

Whatever it is, scent rolling must have conferred some sort of selective advantage over those that didn’t roll, in the evolutionary history of the common dog ancestor and is still an important behaviour to the dog.  It is therefore, a normal and natural part of a dog’s life. They enjoy rolling or they wouldn’t do it and it may be something they just can’t help. 

So, can we stop this inherently normal and seemingly important behaviour?

Well as always ‘it depends’. It depends on how far away the dog is, the lure of the scent, how well we have trained a recall and how concerned we are about the smell. Perhaps we should just let it roll. After all, we cover ourselves in smelly stuff all the time. We roll it on, wash it in and spray it all over and often pay a great deal of money for the privilege. Studies have shown that humans feel more confident when wearing scent and it too conveys a lot about the environment we live in and other social information such as wealth and success. So before we get too upset about the preferred scent choice of dogs perhaps we should allow them some leeway, because after all they do seem to really enjoy it.