So when she was a pup, you used to let her poop in your neighbor's yard, and didn't clean up after her. I'm sure that made a wonderful first impression. Now, you're still letting her run around unsupervised for hours at a time, in the dark, but you say "she wont go over there now even with out the collar," which says to me you're letting her out without it. So how do you know she's not going over to his yard? She's a Lab; she's smart enough to know she's not going to get zapped without the collar on. Even with it on, a lot of dogs will run through it. Almost as important, under the law, that's not a fence. If your local ordinance says you have to have your dog fenced in, and it doesn't address electronic fences, than you are required to provide a physical fence, not an electronic one. Sorry Stoner, but based on what you have posted, it seems to me you're not acting responsibly where this dog is concerned.

All that said, your neighbor's beef is with YOU, not your dog, and no matter what's happened, he is entirely in the wrong coming onto your property and beating your dog, who is just doing what dogs do. Anybody who would take out their anger on a person's animals is beneath contempt.

OK I'm off the soapbox now... You originally asked what to do. I'd say do some research, check on what the local ordinances are, and make sure you're on the right side of them. If your neighbor attacks your dog again, defend your property as you deem necessary (remembering that, under the law, "property" is what dogs are), then call the cops.