Muzzles are sometimes used on untrained dogs, large or small, to prevent either unwanted biting or unwanted barking. They can also be used on aggressive dogs or other animals. They are usually made with a strong buckle or other fastening device to ensure that they do not come off accidentally.
Muzzles can be primarily solid, with air holes to allow the animal to breathe, or formed from a set of straps that provides better air circulation and allow the animal to drink. Leather, wire, plastic, and nylon are common materials for muzzles. The shape and construction of the muzzle might differ depending on whether the intent is to prevent an animal from biting or from eating, for example.
Dog muzzles can be found in most pet supply stores.