Those reasons can involve the bladder, the urethra which is the tube from the bladder to the outside, or incontinence can be caused by abnormalities in the parts of the brain and spinal cord that control bladder function. Related anatomy dog/cat
Incontinence can be confused with diseases that cause a pet to urinate frequently. This pet health topic only discusses incontinence, not frequent urination.
Incontinence can also be confused with submissive urination. Submissive urination occurs when a dog is acting submissive to a person or to another dog. Submissive urination occurs more frequently in young animals. The dog usually rolls on its back and urinates. These dogs can also urinate normally.
Learn more about urinary incontinence from the WSU veterinary library: