Like others have said, ideas are a dime a dozen. Execution is what matters. Most apps nowadays can be (rudimentarily) recreated over a weekend - it's likely that almost nothing you are doing is so revolutionary that is should be considered a state secret. If you are THAT worried, it could be a sign of insecurity in your ability to execute on the idea, not the threat of losing the idea itself to someone else. Keep that in mind.
Think of it this way, the Twitter technology itself was not exactly revolutionary and there were literally thousands of copycats after it launched, but their execution is what set them apart and helped them gain the traction they needed.
If you don't have the skills get them... its the fastest course, and it shows your serious.
Bad and working is worth a lot more than an idea on paper.
Ideas are a dime a dozen. If you think you're going to find someone to build an application/product for you for free, you might reconsider your idea because I'd say you already aren't thinking clearly.
As zer00eyz said, if you don't have the skills, get them.
I have never seen a wire frame, or a bar napkin, or a business plan or any sort of competitive analysis come back from one of these proposals.
Lets flip this on its head. I have an idea, and I'm doing all the coding/dev work. What are YOU going to do to add value to that endeavor? How much would that work be worth as a percentage?