Anal gland removal is the surgical removal of the dogs anal glands, located on either side of the anus. These glands secrete a pungent smelling odor when the pet defecates or is frightened or alarmed.
Anal sacs, or anal glands, carry some smelly fluid and occasionally need to be expressed, or emptied. Many dogs express them by themselves every time they poop the sacs are around a dogs anus but occasionally the sacs fill with fluid and your dog needs some help to release the fluid.
When you catch your dog dragging his behind, he's not using the lawn for toilet paper. His anal glands are full, and he is trying to relieve the pressure. Most dogs naturally empty the little sacs, located under the skin on either side of the anus, during bowel movements.