Cows (specifically, the African Ankole-Watusi breed)
Cows, especially the African Ankole-Watsui breed, are extremely protective breeds and can get intimidating and aggressive when it comes to protecting.
Geese
Known for their loudmouth and aggressive behavior, geese make excellent guard animals as they are protective and territorial.
Llamas
Llamas are protective and loud. They make fantastic guard animals, especially for sheep, as they protect them from coyotes.
Donkeys
Donkeys are surprisingly territorial and can get aggressive to protect their boundaries, which makes them great guards.
Ostriches
Their intimidating size and aggressive behavior make them effective against intruders and predators.