Though dogs and cats have historically used their anal gland secretions to mark their territory, our pets often express these glands when they're anxious or frightened. Pets so affected experience a build-up of fluid in their anal sac. If your dog's anal glands are full and/or impacted, your vet can express the fluid with their fingers. If this becomes a chronic problem, your vet. Your dog's anal glands may spontaneously empty just by walking around, Normal anal gland fluid ranges from yellow to tan in colour and is watery in.