Startup ideas are worthless. Execution is everything.
Every day, someone posts on /r/startups about how they have a really great whiz-bang secret idea that will revolutionize everything and make them billions of dollars. Now they "just" need some investors so they can hire contractors to develop it. But they can't say what the idea is, of course.
It's secret. Can't talk about it in public — someone might steal it. They have to get an NDA ready before even pitching potential investors. They have to get that contract dev team going ASAP before someone else thinks of it.
The reality: It's likely that 10 other teams are already working on that exact idea. if your idea is any good, 100 companies will clone it the minute you launch publicly anyway. And that's fine. Fortunately, ideas are worthless. Execution is everyting.
If you're the only one with that idea... something's wrong.
Very few startups die because someone stole their top secret idea before they could launch it. Tons of startups die because there just is no market for what they build; there's no way to derive a profit from doing whatever it is they propose to do. If there are competitors in the space, that means others at least think it's possible to make a profit in that market. That's a good thing.
It is extremely unlikely that you are the first one who ever thought of your whiz-bang secret idea. The rest of the world is looking at the same data as you. While most probably don't share your insights, if these insights are correct, it's likely that at least a few do. There are a lot of people out there.
If the idea has any potential, there are probably 10 companies around the world already doing it. And that's fine. Most of them will be very bad at executing it, so you can out-compete them on the execution.
If nobody else is already doing it, you have to very seriously ask yourself what all decent investors will ask you: Why not?
Is there some barrier here that you haven't perceived? Do you have special skills, special knowledge, or special access to this market that nobody else has?
If you don't have an excellent answer to this question, you're doomed before you even start. It's possible that there is a perfectly legitimate reason why nobody else has done it before, yet you can do it now. You need to know exactly, and in detail, what that reason is. (Hint: it's probably not "I'm so amazingly insightful that I just thought of it first"!)
You are (probably) not a unique snowflake
Your barriers to entry, your Thielian moat, exist in the execution phase, not in the idea phase.
Here's a legitimately great startup idea that you can have for free: "Give users a list of relevant web pages that provide information about a search query they've entered. Show ads next to the results."
It's not a secret idea. This was a great idea when Google did it in 1998. It was also a great idea when Yahoo, AltaVista, Excite, HotBot, Lycos, Infoseek, Inktomi, Ask Jeeves, and dozens of other companies you've never heard of did it years earlier.
Google didn't win because they thought of a top secret idea that nobody else had. The idea wasn't secret or even new when Google did it. There were already tons of companies making money doing the exact same thing. Google just executed the idea much better than those other companies did. That's all.
If you execute better than Google today — that is, build a search engine that usually returns better results than Google does now — everyone will switch to yours overnight. If you build a better social network — one that's easier to use, in some sense, than Facebook, and where most people's friends are already on it — everyone will stop using Facebook and use yours. It happened to Friendster and it happened to MySpace. Remember them?
This is, of course, hard to do in an established market with a big player who is already executing pretty well. That is how you establish a monopoly in the Peter Thiel sense — execute so much better than everyone else that it'd be very hard for anyone else to approach your level of execution.
There likely isn't already a big winner executing well in the market in your case. There are probably 10 or 20 Friendsters and Lycoses out there, not one Google or one Facebook. That's a good thing!
Be the Google in your market.
Be the Google, be the Facebook of your area. Trying to avoid competition by meticulously securing your idea is futile. At the very least, you can't keep it secret after you launch to the public, which is the entire point.
Rather than wasting energy trying to secure NDAs and keep secrets to avoid competition, embrace competition. Competition means that there's actually a market there. Learn from your competition so you can out-execute them. Rather than trying to avoid competition altogether, focus on making your customers the happiest of all customers in the space.