Cal. Food & Agric. Code § 31642

A potentially dangerous dog, while on the owner’s property, shall, at all times, be kept indoors, or in a securely fenced yard from which the dog cannot escape, and into which children cannot trespass. A potentially dangerous animal may be off the owner’s premises only if it is restrained by a substantial leash, of appropriate length, and if it is under the control of a responsible adult.