I have been explaining to Master 9 since Inca arrived that he can't leave stuff on the floor of his room etc. He either cleans up as soon as he's finished playing, or closes his bedroom door until he does clean up.
Walked into the hallway before and he's sticky-taped an A4 sign on his door "Do not enter, Inca."
Husband and I are laughing oursleves silly, trying to explain that dogs can't read. Silly boy!