My little guy will NEVER knowingly be put in any dangerous situation by me. Whenever we are approached by a large dog, for example, he is almost always behind me looking for ME to protect HIM.
His most important function in life is his ability to detect anything which he doesn't think belongs in his area. He has never bit anyone to my knowledge but he will snap at unwelcome advances from strangers. Once he is properly introduced to someone, he is your friend for life.
I would have been alerted the second he found out someone was jumping the fence. It is amazing what he can detect even when he is inside. In a discussion with another chihuahua owner last summer, he contended Chihuahuas were bred for the wealthy in Europe so that pickpockets could not steal their jewelry. It's my first small dog and he is an incredible first alert.
A lot of people make fun of Chihuahuas (probably because the name is funny to us) but I hear they are quite intelligent and fun to own!