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That is very possible that he cannot control it. If he has a Urinary Tract Infection the urine can come out suddenly for them and they cannot stop it. A visit to the vet can confirm or deny this prognosis. It is important that he go to the vet because he needs treatment ASAP because UTI like symptoms can be caused by bigger problems and UTI's left untreated can lead to bigger problems. For more info see:
If it turns out it is not a UTI then you may want to reguate his water intake and take him outside to urinate more frequently until he gets a little older and can hold it better.
With UTI's it can affect them in different ways. I have a dog that just recently recovered from a UTI and she would have non stop accidents some days and other days would have a couple or none at all. Also, she showed no signs of pain the entire time she had the infection and she did not have any problems urinating either. It can effect them one way some days and other days differently and can differ from dog to dog with some general consistencies. Here is more info on UTIs and other incontinence problems.
It is best to have a vet check him out as he or she can rule out any physical reasons for the problem and if none are found can give you suggestions for how to solve this problem.
Hope this helps!