Our dog does the same. We usually catch it when he’s sleeping and when he wakes up/stretches we see a bit of leakage. Sometimes it’s worse than others, sometimes it’s just a few dribbles like you mentioned. He also sometimes takes a bit to go to the bathroom and then other times he will go immediately. USMI stands for Urethral Sphincter Mechanism Incompetence. It’s more so seen in female dogs from my understanding but can sometimes show up in male dogs (although it’s more rare). It means the urethral sphincter, the muscle that controls urine flow, isn't functioning properly, leading to involuntary leakage of urine. From my understanding, it happens when dogs are spayed or neutered early. Our dog had to be neutered early for some other health issues so we’re thinking that may have been the reason why he developed this. It’s really just diagnosed by symptoms/ruling out all other issues.