It is very, very hard to beat a good, large guard dog inside the house. First, they pick up on the faintest noises/smells. Second, they alert you quickly and pinpoint the threat. Third, they attack an oncoming intruder giving you precious seconds to arm yourself.
I have one of those. He’s really a marshmallow once introduced... he likes to lie on top of his crate (level with the windowsill) and watch the outside. Those long pointy Shephard ears are a pretty good deterrent. And a sign that says “Dog on duty...takes job seriously”. ;-)