I think it is a Chihuahua thang. They are very very smart dogs. He is doing some kind of marking. I think isolation when caught in the act can work with them. Remove from the scene of the crime and put in a pen or small enclosed room. Others who have had Chihuahua may or may not agree with me but I think tthat they understand the cause and effect thing better than pugs. My Chi used to be able to tell by what I was wearing if he had a shot of going with me. If I was in my work clothes, he moped on his dog bed ignoring me.