German Shepherd Dog
The GSD is pretty much the most trusted guard dog breed. They rank among the smartest breeds and they’re able to learn an almost infinite list of tasks.
Temperament: German Shepherds are highly active dogs and described in breed standards as self-assured. The breed is marked by a willingness to learn and an eagerness to have a purpose. They are curious, which makes them excellent guard dogs and suitable for search missions. They can become over-protective of their family and territory, especially if not socialized correctly. They are not inclined to become immediate friends with strangers. German Shepherds are highly intelligent and obedient. – Wikipedia