If what you are worrying about is plagiarization instead of pirating, then I'm afraid that there's very little you can do. You can't patent game mechanics. Rule books can be copyrighted, but the idea behind a rule book can't. You may try writing something like "any one played this game agrees to not make a similar game" but even if that's enforceable (which I doubt), people with enough money can easily hire something to do a clean room implementation.
So, I think the best (and probably the only) way to deal with this is to make your game good enough, then you don't have to worry about plagiarization at all. If your game is good enough, people will come to play and those copycats might even help bringing more players (e.g. see how the popularity of 2048 helped the similar original game Three).