It can be a urethra blockage. My chow had it he was younger so I assumed UTI, had he been elderly I would have thought old age but because he was just a young guy I was concerned he had an infection. I took him to the vet and she said it was good I didn't ignore it because they can be very troublesome if left unattended.
I remember at the time I had to walk him often ~ we did a lot of walking I was pregnant with my first who turns 23 this December but I still remember Cheech having this. And I remember she gave me a solution in a bottle that I had to clean the area with several times a day.
I'm not saying that is what your dog has, I just know the above is what I dealt with a chow 20 some years ago. We've never had a dog in the family since then that had that, nor have any of the neighbors so I am guessing it isn't very common.
Because of what I dealt with though, I would advise you to call your vet and have him looked at.