Years ago someone asked convicted criminals what they were most afraid of: large barking dogs and the sound of someone racking a shotgun.
I don’t rack to warn. There’s always one in the chamber, and they’ll never hear the safety moving to fire.
Racking a shot gun is the key
The guard dog combo I would recommend is one little yapper dog (deterrence) and a chow chow (sneaky and vicious if they still keep coming and enter the premises).
The chow chow does a soft roar like a lion—but you would never hear it above the yapping of the little dog.
Chow chows supposedly were the guard dogs of choice of Genghis Khan.
A dog is the #1 deterrent to home invasions.