Here is a good article for potential urethrostomy patients. Warning: there is a photo of an incision site that might make people uncomfortable.
Urethrostomy in dogs
Here is a link to a technical article about the procedure that is probably behind a paywall for most people. If you have the procedure done, I can copy and paste the section about post-surgical care.
Urethrotomy and urethrostomy in the dog - ScienceDirect