How do I stop my two year old adopted dog from urinating in the house?

I just adopted a er spaniel/dachshund mix from the dog pound 7 days ago. He is very well behaved and seemed to be housebroken until today. I always leave water down for him and I feed him twice a day. He has urinated two times today near a window. There are bushes outside of the window so I wonder if he is trying to mark the bushes. Today is the first day that I have opened the shades for him. Also, he was neutered two days ago. What can I do to make him stop without being too harsh.