I scrutenized the OP's original account. Predator could also have been a badger.
Regardless of perpetrator, try to think of layers in your predator management. It is very diificult if not expensive to deny all predators access to your flock all of the time using housing structure alone so make it so bad guys have muliple obstacles to overcome. In OP's case, the perp accessed the coop by burrowing under the buried perimeter fencing so it got in and got ALL birds. Think about how perp came into contact with birds. It had to do so or birds would not have been harmed. I ask where did contacts occur, on roost, ground, against perimeter of coop fencing or wall? Also distinguish between initial contacts and where killing actually took place. Many predators that dig well do not climb or jump well. If perp was a badger or racoon, then consider protective value of roost. How can the roost be constructed or placed to limit the predators access to birds? Remember most chickens have at least a limited capacity for flight, usually at least 6 feet vertically. Setup roost so birds can get up there by flying but a dumpy predator like a racoon, badger or oppossum can't. You may not save all birds but losses will be more limited until another layer can come into play such as your dog, or you packing a boomstick. Also as another mentioned, keep live traps set almost continously as that will catch some potential perps. The electrical fencing is also a sound idea if already in use with other livestock. Also, do not forget to get out there and check on things periodically at night.