I don't think putting a doberman in a small room with no light (window blinds shut off from the outside light) and the door shut. That is kind of cruel isn't it? Doberman are family dogs and people pleasers. I bet he is super excited when he is let out!
He should be crated in a good size wire crate regardless of if you feel he has learned his surroundings or not. Dobies are an intelligent breed that needs constant stimulation and socialization. This being said, they get into all sorts of trouble when alone, especially in a big backyard or vacant house.
Is it possible he is urinating out of fear? Do you know the conditions he was in prior to rescue and rehoming?
- Wire crate
- Crate when not home/sleeping
- Routine, routine, routine!!
- Crate in open area of the home where he can see everyone/the other dog/etc.
It will come soon enough. Maybe he needs an extra walk to help him understand he "goes" outside. But please go and get him/borrow a crate from a friend and move him out of the room you are keeping him while you rest/sleep/go to work.