The world out there is already a cauldron of ideas, every one possess one. What differentiates successful and not so successful individuals is courage to speak, share, and execute ideas. It's one of the biggest myth that somebody will steal your idea. Since, it's your idea no one else can understand the DNA of the same as better as you. The world out there wants a business model to copy than idea.
If you feel a "Non Disclosure Agreement" might prove to be the much needed panacea then you're already on a path to achieve euthanasia. So, rather than focusing about copy cats, focus on how you should present it as an opportunity. All the best!!!!