The Root of the Behavior
Most often than not, dogs roll on their backs to alleviate an itch. Unlike the area behind their ear which they can reach with their paws, their backs are difficult for them to reach. In case of a back itch, their only means of satisfying it is to roll onto their back and move around in hopes of an improvement or to rub themselves against different pieces of furniture. It is also why dogs will sometimes roll around on their back during a walk in the park, the coarse grass works like a hairbrush that diminishes and relieves them of the itch. If your dog is rolling around on an object he might be using it to scratch himself or to mark it as his own.
Though occasional itching is normal, if your dog rolls onto his back to scratch a particular spot frequently it is best to investigate it for possible ticks or fleas. If your dog rolls over onto his back during playtime with you or other dogs, it can be safe to assume that it is either his way of waving the white flag and submitting or a tactical way to avoid getting bitten and assume a defensive position. It’s a trait that has remained through evolution and shows that a dog has good communication skills. Exposing the belly while being on their back is one of the ways wolves show respect to the pack leader. Hence, if you have recently caught your dog ruining your favorite pair of sneakers and then promptly rolling onto his back in submission - your dog is most likely using the roll to admit to his bad behavior, as an apology and a sign of respect. He knows he was caught in a compromising position and your tone of voice lets him know that what he was doing was wrong. Rolling on his back is his way of showing he does not want to fight, that he trusts you despite your anger, even in his most vulnerable and unprotected position.
However, if your dog seems to be happy or relaxed and starts to expose his belly after some back petting it can be taken as a clear sign that he wants you to rub his belly. Your dog might also be rolling around on his back because it feels pleasant or because he’s happy and feels safe enough in the environment to have his belly exposed.
Encouraging the Behavior
A dog rolling onto his back on a hot day could be attempting to cool himself down. Make sure that your furry friend always has a full bowl of fresh drinking water and some shade, especially during the summer. It is perfectly normal for dogs to roll over onto their back, even though they do it for different reasons at different times. Regardless of breed, it will happen occasionally and it is neither the type of behavior that should be encouraged or discouraged. However, if you notice it happening frequently you need to consider seeing a professional. In case it resembles an itch or some sort of skin irritation you should take your dog to the veterinarian to rule out fleas, ticks, allergies or dry skin - all of which can and should be treated.
It is also strongly recommended for your dog to see a dog trainer if you suspect your dog is rolling onto his back out of fear. For example, as soon as the vacuum is brought out of the closet or in case of other phobias. If your dog has rolled onto his back out of fear, it is best not to touch him and instead to stop whatever you were doing that could have scared him, to walk away from him and to keep talking to him in a calm, soothing voice.
Other Solutions and Considerations
Dogs use body language as one of their ways to communicate with you, that is why it is very important for you to be able to differentiate between the different range of behaviors your dog exhibits to be able to best understand him and when required, to help him. You need to be able to tell when your dog's belly-up position is just him thermoregulating or when he is asking for attention and belly rubs. And in case his back rolling becomes frequent or concerning, be sure to take him to the veterinarian for diagnosis of the underlying trigger and its treatment.