What kind of dog is Duke? The way we house trained our poodle was we put newspapers down for her at first (in the house) and when she went on them we would take them outside with us when we took her out and then she would smell that and see that's where she had gone before and then she'd use the bathroom outside instead of in the house. It took time but she is now 6 yrs old and never uses the bathroom in the house!!!

Also putting him in a crate/dog carrier would be a good idea too. Just only let him out when you're playing/feeding him or taking him outside!