Does he have free roam? Treat it as if he was a puppy and your doing potty training all over again, starting with the basics. It sounds like you got Parker around the same age I got Kaji. Kaji was 12 months and an expert at marking. What I did was restrict his access to the house. He was allowed to roam only when I can give him my full attention. He did wear belly bands, but I only used them for a short period of time. I used them so whatever small amount of pee he was able to squirt would be captured and the furniture, or wall, or appliance was safe. I did walk around behind him as he was exploring his home. Whenever he did lift his leg, I corrected him. I did a double clap followed by a firm (but not yelling) "no." He was also on a strict potty schedule. I followed it everyday, and praised him immensely for peeing and marking outside. I wanted him to understand that it wasn't the act of peeing or marking that was bad, it was where he was doing it. He is now the perfect little gentlemen. I do keep belly bands on hand for when we go visiting a new house. The first time we visit is when this little guy decides to lift his leg.
Every time after that he's ok.