Ruby and a sheep
Being a guard dog can be a tough job, but somebodies gotta do it and most dogs that have that position take great pride in what they do. Dogs love it when they feel useful and have a task that they need to fulfill at all costs. It is in their nature to want to help out and pull their weight.
This dog named Ruby was too old after many years of being a guard dog to do her job effectively anymore. So she ended up in a shelter with other animals, but no one thought this would happen. She started to protect and look after other animals in the shelter, especially her friend, a baby sheep.