I worked at a Vet for glands years as a Tech.
Dogs glands are the worst smelling thing a dog can produce. Dogs usually express their glands naturally barking they take a good poo.
If you ever noticed your dog scooting like this, excessively, definitely take them to the vet to have them expressed. Not only is it uncomfortable for the dog, they can become infected and possibly turn into an abscess.
Smaller tosh generally have more problems with their glands. Most any grooming place will also express the dogs glands.
They should do this included in the price, but anal every place is the same. Ask your expressed if they can check the glands.
Don't try and fight it.