Thank you for asking again about your dog.
My name is Rebecca, I am a veterinarian, and will do my best to help you.
How long ago was the surgery? Is he doing well afterward, no problems like weight loss, vomiting, or diarrhea?
It is possible that there could be adhesions attached to the bladder that could cause the urine dribbling.
Starting with a urinalysis still would be the best place to start, to be sure there are no crystals, or infection in the bladder or kidneys.
If that is normal, you could have an ultrasound of the bladder, to see if there are any adhesions or other problem in the bladder.
Trying the PPA (phenylpropanolamine) to improve the bladder sphincter tone would be a good thing to try.
We see this problem more in older female dogs, because of reduced estrogen in their bodies. Using the PPA or small doses of estrogen can help. It is not as common in male dogs, so doing an ultrasound still would be a good idea. I did once see a male dog with this problem that improved with estrogen therapy, so that might be worth a try as well.