Yes! Aside from designated trails and parks, you must leash your dog. Off-leash dogs can become confused by bikers and skiers. If a dog crosses the path of even a slow moving skier or biker, significant injury can result to person, dog or equipment. Confused animals can also do things their owners do not expect, like biting. Don’t find out the hard way that your nervous dog is a biter. Damages and injuries will likely become the liability of the person who allowed the dog to be off-leash. A dog owner found in violation of leash laws, could be sued!