The fastest dog breed in the world is the greyhound. Greyhound dogs can reach speeds up to 45 miles per hour with unsubstantiated reports of exceptional greyhounds reaching more than 50 miles per hour.
The speed of greyhounds means that greyhound owners must take special care of their pets. According to the Greyhound Pets of America's Minnesota chapter, greyhounds should never be left tied to a tree because if they begin to chase something, they can seriously injure themselves when they reach the end of their lead. Similarly, invisible electric fences are a bad choice for greyhounds because the dogs run through the invisible barrier too quickly for it to deter them. Greyhounds should never be allowed off the leash in public because they are several times faster than a human and can easily lose their owners.