Silly me! I forgot to give you the link to Robert MacDowell's website:
http://www.herbal-treatments.com./articles_treating_canine_incontinence.html
This could be a very helpful website for you to visit. It is written by Dr Robert MacDowell (herbalist) and does give some herbal remedies. However I would advise you book a one-to-one consultation with a Herbal Vet because a full medical history ought to be obtained, and a qualified medical herbalist consulted before herbal treatment is started (that would apply to Humans as well as Canines) Herbs, though natural, and often without too many side effects, are powerful chemical compounds that might, or might not suit the patient, and can clash very badly with any prescription medicines.
Acupuncture is another avenue you could explore. I have heard that homeopathy can have results but am sorry I don't know which remedies would be used.