I keep three vicious "attack pit beagles" on duty here aged 9 years, 3 years, and 5 months old. (Shiloh, Hunter and Cody) Anyone coming here gets sniffed for milk bones and liver treats.
i have 3 Jack Russells on the job (down from six- ). they have successfully alerted us to and subsequently repelled 27,482 of the last ZERO attacks on our property. they are thorough, if not terribly discriminating in their vigilance...
i live more frugally; my cat only eats the rats and mice here. no fluffie chow for her. she stands on alert, 24/7, awaiting the chance to walk around your leg. this way she determines if you pose any threat.
My guard cat, Koshi, will grab your calf muscle as you pass by, giving you heart failure and protecting the shop quite well. I would advise calling before coming by.(but that might not help!)