It really depends on where you live. In many states, the value of livestock destroyed by dogs is set by law. In Virginia, it's $10. It doesn't matter what the breed is. (
https://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+3.2-6553)
First, you want to call the police/animal control, and file a report. This absolutely needs to happen - it's your legal grounding if you need to dispatch the dog at some point.
Second, tell the neighbor that if the dog is in your yard again, it will be dispatched.
Third, put up fences. It's his responsibility to keep his dog off your property, but it's also your responsibility to protect your animals, and if the neighbor's dog can get to them, so can every stray dog that comes by, and every coyote or fox around.
EDIT:
Virginia also has a "Dangerous Dog" classification, and one of the ways a dog can be classified as dangerous is 3 livestock issues without the livestock owner killing the dog in the act (which we have the right to do) - if a dog is classified dangerous, the owner needs to register it with the state, needs to be insured to keep a dangerous dog, needs to keep it in a locked, inescapable area, etc. This is another reason you need to report every incident - if you don't report, you won't have legal grounds.