nossond:
Nothing against you, but why do you say that the dog or pit/bor is due to Poshya vs. Mammono Hamazik?
MAmmono Hamazik is that you are responsible for your object that damages, except whan you are an Ones (such as the gate falling down in a hurricane (First Mishna in HaKonyes)). Bor is due to either you owning the Bor but not the surrounding area or it being Halachicly owned by you, just like Chametz on Pesach (R’ Elazar Besham R’ Yishmael (29b)).