What is the exact phrasing of the law of "Finders Keepers"?

I am preparing for my court case next Monday and think this piece of information could be crucial to my case. Its a long case so I'll give you the short and sweet version: 1) I found a small black dog in my backyard. 2) My neighbor seems to think it belongs to him. 3) He claims it answers to the name... show more I am preparing for my court case next Monday and think this piece of information could be crucial to my case. Its a long case so I'll give you the short and sweet version:
1) I found a small black dog in my backyard.
2) My neighbor seems to think it belongs to him.
3) He claims it answers to the name "Shadow," but after numerous tests, I disagree. *I'm planning on doing the test in court to wow the jury*
4) Also if the dog happened to be his at one point in time, by the law of Finders Keepers, it is now mine.
5) The neighbor has a wife and two small kids, so I think he would be too busy to adequately take care of the dog.
So as you can see I've got a pretty solid case here, but I really want to drive it home with the exact legal definition of Finders Keepers, which has been hard to find. Any lawyers or Law and Order buffs out there?
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