German Shepherds are very strong and handsome dogs. They are known for their courage and loyalty. They have a strong protective instinct, and must be firmly obedience-trained from a young age so they will not be overly aggressive. The breed is extremely intelligent and has been use as guard dog, sheep dog, in police and military work, and as a guide dog for the blind. Their sense of smell is so keen that they can sniff out underground mines, drugs and intruders, and gas leaks in pipes buried far underground.