There's only so much you can do to convince him to go. If you had PD there, they may have been able to help - i.e. he goes with you or gets arrested for the pot. If he was A&O x3, and continued to refuse, there's nothing else for you to do. I would have made sure there was someone to stay with him for a few hours in case anything changed, though. If you're still worried, and you have a good relationship with the PD, have them do a welfare check a few hours later.