Is he neutered? Male dogs that are not neutered like to mark. Even sometimes after they are neutered, they still mark.
It may still be too early to let him have access to another area. Once you introduce him to another area you have to keep him tethered to you just like you would when you first start potty training. Once he starts sniffing you take him to his spot. Also, make sure you take him potty before he goes into the new room, and then take him out to go potty again after 30 min or so. Hope this helps some.
