I'm, this is a personal opinion, agreed to the holding of a personal weapon at home, which would remain for the "recreational shooting" or our own protection only in the perimeter of his property.
In this case it seems to me that this Marine should not incur a fine, he defended his family of a threat that could potentially, or critically, injure one people. I had many neighbor that holds aggressive dogs only who obeyed to their masters, and it often happened that they escape from their enclosures. What is normal in the West Indies, but the problem is that these dogs then shows dangerous for pedestrians at night.