Pets

Both German shepherds and retrievers have to be taught to be nasty. They'll bark but the only protection they generally offer is trying to lick an intruder to death.

Then again, I've been pals with junkyard and urban theater guard dogs, usually to the owner's consternation. Big dogs aren't averse to making noise, but they're generally not averse to making friends. You really have to work at it to turn one nasty.