Need advice about male dog marking in the house

My mom and dad purchased a trailer to move my Gram closer to us. Today we went to her house to start moving her things and noticed exactly how bad her home smelled. We knew that she had a problem with her yorkie peeing in the house, but I didn't realize the extent of the situation. She had pieces of wood furniture that were completely ruined by dog pee. We were there for approximately 1 hour and I caught her dog trying to mark his territory 5 times. As soon as he started to lift his leg, I gave a sharp sound (like Victoria - on the show "It's me or the dog") and he immediatly quit. The problem is that he is going to completely ruin the trailer if we don't do something. We can't tell my Gram that she has to get rid of her dog. She has had a stroke and is unable to properly catch him in the act everytime he tries to mark. He is NOT neutered, and my mom wants to know if it would help to neuter him now. He is probably 4-5 years old now. I looked at Belly Bands and was wondering if anyone has any experience with them or advice about my situation. Please help, she will be moving in soon and we can't allow this dog to ruin another home. Thanks, Staci