If you are a dog owner don't even vaguely consider letting your dog run free even if it is allowed. I know you think it is "trained" or "friendly". That typically applies only to the perspective of the owner and the situation can be a lot different for a stranger walking alone.
I used to surf fish at night and took to carrying a wicked hand gaff. Hiking on trails a hatchet suffices. It seems the dog owners who assure their dogs are trained and friendly all reconsider when I explain the dog will only bite once.
Aside from the comfort and safety of other visitors, there are other reasons that dogs are not allowed on trails in most national parks. They scare the wildlife. They do not interact well with bears.
