Unfortunately, neutering doesn't always stop them from marking. I know a woman whose ten year old Yorkie started marking when she fostered a dog that marked. They very often learn it from other male dogs which is what may have happened in your case. Sometimes they will start marking their territory when a strange dog visits and leaves their scent in your house.
It's a very difficult habit to break once they've started marking. You probably should put a belly band on him when you visit or he will probably be tempted to mark his territory. |