Well, congrats on adopting a new pooch .

Do you know anything about his history? Is he fixed or intact? What have you tried to do to get him used to the idea of living in a new house? How long was he at the shelter, and did he stay in an outdoor pen, or on a concrete floor, or what?

There are loootttsss of reasons that a dog could pee in the house, and there are loooootttttssss of people that will want to help you on this site, but we do need a bit more information to be able to help you best.