german sheppard - no way - hips...that being said i had a dog i rode with for years, and she was great, always stayed right behind me...she wouldn't run all out but would trot along i just had to wait at each intersection...you cannot run them too much though, if they do not know how to pace themselves some breed will actually run themselves to death trying to keep up.... a good friend of mine has an Australian sheppard that he took riding for many years, she was fast but never paced, to make a long story short, she now has had both her rear legs rebuilt (ACL i think) at $2k per leg and now one of her front legs is going bad....after watching all of that i would not bring a dog on any ride unless i knew it could pace itself and i would keep it very, very short with lots of rest in between...also when they are puppies they cant do too much either...good luck and be careful..
as for people who are afraid of dogs being off leash, get a grip, if you see a dog off a leash you can make the assumption that it is friendly 99.999% of the time, dogs get a bad deal, maybe we should all spend some time on a leash and see how it feels...they need to run just like we need to mtn bike..a walk on a leash doesnt cut it..