Inside a National Park there is a pretty substantial fine for not having your dog on less than a 6’ leash, but the bad thing is it can be a ticket and a mandatory court appearance which can put a kink in your travel plans especially since it is a federal court several miles away. Generally rangers just warn people to abide by the rules, but after years of warning the same slow learners sometimes experienced learning is a better alternative to a ticket and a 150 mile drive on a day not of their choosing. Be aware of the rules where you are staying and follow them, there is good reason for the rules.