I cycled across the US with my 45 pound girl, Fiji. At first, she could only run about 1 or less miles per day. After a few weeks, she was running about 20 miles per day, with breaks in between, of course. I used a Doggy Ride trailer and Springer America attachment. I loved both, and had little to no problems crossing the country with both products. On a few occasions, other dogs gave chase and Fiji broke the plastic attachment on the springer trying to get to them. Otherwise, it was very hard to break. As far as dogs go, if you have no fear, do not panic and show a bit of backbone, most dogs respond well to using the bicycle as a barrier and a loud, assertive tone of voice. I never had a dog still keep coming at me after I declared "No" for both them and my dog to hear. Usually Fiji was instigating the chasers, barking, growling and whining at them. But they still listened to my stern warning. Now, I am not quite sure what I would do with a bear. Lol
Another thing to think about is your dog's personal stamina, joints and pads. I used mushers wax on Fiji ' s paws to protect her pads from great harm. Running on concrete can devastate a dogs paws and joints. So, I would suggest doggy shoes or wax. Also, some breeds can run for lengthy amounts of time. It helped that Fiji is part Whippet. My rottweiler on the other hand died from over exhaustion on a short walk several years ago. Just like you would for a human, you need to get clearance from your vet that your pup is healthy enough to partake in bicycle running. I have heard of many owners exercising their dogs to death, with good intention.
I hope this helps.
