Since I work with dogs for a living (in a training/boarding facility) my suggestion would be to research the history of a breed and find out what it was bred for initially. Most breeds were bred for working or hunting, and sometimes both. Whether herding, retrieving, or draft animals, dogs were built/bred for stamina and strength. With all that in consideration, there are literally millions of dogs in need of rescue in local shelters and through local rescue groups. And I have yet to meet a dog that disliked the trail. Some might be just better built for long distance.