Dog pees constantly

Question
I have a black lab who is almost 7 months old. He is housebroken, letting me know he has to go out by sitting by the door, and whining if I do not come right away. Since he was about 4 months, he has had an issue where he cannot always hold his urine. He has to pee at least every 1.5 hours. If you don't take him out enough, he will pee in the house, but he doesn't even realize he is doing it. He will run around and there will just be a trail of pee behind him. He has peed walking up stairs, while playing with another dog, and even while sitting. He won't pee while lying down, such as at night or in his crate, but as soon as he gets up I must rush him outside. We have been to the vet numerous times, he has no evidence of a UTI, and he blood tests have all come back normal. I think it could possibly be a muscle issue, but I was also told it could be a behavioral issue.  It definitely isn't marking though. Do you have any ideas or suggestions?
Thank you in advance for any help or ideas you may have.

Answer
I think I would check with a different vet as a first step. It COULD be excitement, but with males,....not usually. Until you get it figured out, belly band him. Use vet wrap, or an ace bandage around his belly with a kotex inside to soak up the urine. I would persist with vetting until the problem is solved. It COULD be a muscle issue or stress incontenence. Does he cringe and act afraid when he pees like that? The fact that he has to RUSH  outside doesn't sound to me like a behavioral issue
good luck
Cindi