That old phrase is that possession is 9/10ths of the law. While I’m not sure if that phrase holds any weight in court, I do wonder how many times you have to crap all over a building before the owner will definitely NOT want it back, thereby making it yours by default.
I wouldn’t know as I’ve never poo’ed on the side of a building.
I believe this is called “making it yours by deposit” not “yours by default.”