Recently, my doggie son Alvin, a Bichon Cockapoo, started dragging his butt on the floor every few hours. If you've never seen this behavior, you'd find it a little weird.
In Al's case, since he continued the dragging for 2 days, we took him to the vet. Turns out that was a good thing, cause he had an infection of his anal glands. The dragging relieves the pressure created by inflamed glands.
The vet expressed the glands and tested the fluid expelled. Since the fluid showed infection, he gave us antibiotics and this scenario: if the infection does not clear up, the vet would sedate Al, and inject an antibiotic right into the glands. And that's not the worst scenario - if Al continues to have infected glands, they may need to be removed.
Now, Al's vet always paints the worst possible scenario. Al's currently doing fine - the medication seems to be clearing up the infection.
Turns out many dogs (and poodles are suspectible - Al is part poodle) require anal gland expression periodically. Obviously, it's best that a vet does the expression because if the fluid is infected, testing can occur immediately. But because of the cost, many owners express the glands themselves.
Since the glands help expel fecal matter, a bulky stool is a necessity. So one way to prevent the problem from happening in the first place is to bulk up the dog's stool. Yup - Metamusil works, but you need to get the amount to give your dog from a vet.
One other preventive measure - pumpkin - the kind that's canned but not spiced. That's helping Alvin relieve himself much easier AND make sure the glands are activated with a bowel movement. A little (a tablespoon) in his food seems to work. Al is a 25-lb dog, so my guess is that more is needed for a medium or large dog.
More about Al's anal gland problem - What To Do When Your Dog Is Dragging His Butt - Part II.