My in-laws had a Chihuahua as the alert dog and a Doberman as the guard dog. Yip yip yip WOOF WOOF WOOF. Took the Dobie on a lot of walks in natural areas where sketchy people were around. Funny enough, nobody tries anything when you have an 85-lb/40 kg dog. They saw me put her on a leash when I saw them and they knew I could just drop it.