At one time it was thought that when dogs drag their rumps along the ground (scooting) they were scent marking because many other species of carnivore do this including the giant panda, both genders of which frequently patrol their territory and rub their rumps against a rock or tree stump. When dogs do it it is not about marking territory. They’ll do it outside or inside the home. Ideally the surface has to be rough or textured for maximum relief.
Anal sacs blocked and irritating
The main reasons why dogs drag their bottoms along the ground is to alleviate irritation by scratching, and a reason why their bottoms may be irritated is because their anal sacs are compacted. One expert said they might also do it when their anal sacs are full. Another reason is to try and free their anal sacs of a blockage.
Note: anal sacs are important to dogs. Each anal gland is about the size of a pea and they are situated on either side of the dog’s rectum about a quarter of an inch inside the dog’s body at the anus. They deliver a strong smelling substance to their faeces just before they pass to the exterior. This gives the feaces a scent message which is their personal identity. Whereas people identify other people through the appearance of their face and other body features dogs do the same by sniffing, head-to-tail. We see it all the time when dogs meet in public places. The first thing they do is to sniff the other dog’s backside. Dogs are fascinated by the odours.
Fecal contamination on backside
A further reason might be a bout of diarrhoea. The bottom area might become messy and matted. This may irritate a dog to the point where he scoots to get rid of the irritation. The veterinarians call this “fecal contamination”.
Veterinarians will also say that tapeworms can cause dogs to drag their bottom along the ground. They get tapeworms by swallowing fleas which carry tapeworm oocysts. You might be able to tell if your dog has a tapeworm because of small rice like segments attached to their fur around their anus.
Another reason given by veterinarians is rectal prolapse. This is when the large intestines adjacent to a dog’s anus is pushed to the exterior because of straining through constipation. You will obviously have to see a veterinarian about this.
Injury or tumor
If your dog has been injured on his bottom or has a tumor, this may cause discomfort which may result in scooting.
A further possibility is an allergy causing irritation leading the desire to scratch the area. Allergies are tricky health issues. You’ll need a good veterinarian.
Postscript: domestic cats do the same thing for similar reasons.