[Maximo]

Is he neutered? Unneutered dogs tend to mark their territory.

How often do you take him out to potty? Does he also have a way to alert you when he needs to go? I wouldn't rely on that alone, but it is good to be aware of the signs, or teach him to ring a bell (jingle bells on the door handle, for instance).

Dogs usually need to pee early in the morning, right after meals, and after anything exciting like playtime or the doorbell ringing. Plan for potty breaks then.

Also, you need to clean up the accident spots with an enzyme cleaner to prevent the scent from attracting him to peeing there again.