Peeing in the house/apartment

by Rose
(Southern California)

I have a 9 year old Coton, male, who is smart, funny, loving, affectionate and of course, ridiculously cute. Unfortunately, he recently started to pee in our apartment. At first, I assumed marking since it is highly likely another dog lived here sometime before us. But it hasn’t stopped after nearly 7 months and now does not seem to matter if I am home or not. He has been checked out medically and vet says issue is behavioral. I use a belly band when I have to leave and sometimes he pees right in that, even if I just took him out and am only gone an hour. The other day I was home and he strolled into one of the bathrooms and let out a stream. I am at a loss at what else to do and this is starting to have an impact on everyday life. He is not alerting me when he needs to go out but never has a problem throughout the night, up to 9 hours.
Thank you for any suggestions and/or if anyone else has come upon this issue.