Cases of word usage

1) a metal frame on the floor in front of an open fireplace; a guard over the wheel of a vehicle (fender)

2) the nose and mouth if an animal (e.g. a dog or fox); a guard of straps or wires placed over this to prevent biting etc (muzzle)

3) a soldier keeping a watch or guard (sentry)

4) an advance group of an army etc sent as a guard against surprise attack (vanguard)

5) a dog used to guard property (watchdog)