N.,
First, I would find a new Doctor.
No really, at this age, your son's accidents, if only occurring rarely, would not concern me but you stating that it is an almost daily occurrence makes me think your Dr. should be doing a few tests rather than just trying behavior modification.
Please ask your doctor for a hormone imbalance test to be done. These accidents may just be a sign of a medical condition that could easily be adjusted with temporary medication. If your Dr. is resistant, ask for a referral to a neurologist (who would deal with hormones and the endocrine system) just to talk about the challenges facing your son with these daily accidents.
Don't fret, it sounds to me like it is not a behavior issue or anything you can cajole your son out of but rather an uncontrollable issue that makes him embarrassed and regretful. You might also want to ask for a referral to a Urologist. My son (3) had issues with pain while urinating and accidents and what we finally discovered was that he was constipated and it pressed on his bladder giving him urgency. Once he went on a daily does of soluble fiber, everything got better. You can find the answer with some determination, just don't let the DR. stop searching until you are satisfied.
Your such a good mom, being so concerned and continuing to look for answers and help about your children. You'll find the solution.
ann m.