Had a client once who ran daily.  Her neighbor's 2 chows got out one day, ran her down a bolck from their home and literally dragged her to the ground.  Only a quick and brave intervention by a neighbor with pepper spray saved her.  She was literally chewed and torn up from  her arms to the ankles with a severe and deep open gash in her thigh.  She felt like she was being eaten alive.  The dogs had torn one kid's pant leg as he jumped over his own fence to avoid them just a few weeks before.  I have two big dogs and have been around them my entire life.  Chows are among the few dogs that make me uncomfortable.   RTR