While safeguarding the core idea and strategic direction of your concept is important, asking a prospective technical co-founder to sign confidentiality or nondisclosure agreements is not at all practical.
The key to building and attracting any talent to your new startup idea is to create an enticing enough pitch out of it. Perfect the pitch and it will reverse the power dynamics of your recruitment process. Instead of your team looking for value from others, others will be looking for value from your team.
For an example, take a look at DropBox's intro video. The idea that is pitched is very broad without going into specific details on how they're going to accomplish their desired solution. And by keeping everything in broader terms, you essentially protect your core strategy without compromising it from getting stolen - as duly noted by others within the community, highly unlikely.
"But, what if my pitch isn't enticing enough?" - Then all the networking and convincing in the world won't get you anywhere. How are you going to expect investors to invest into an idea that developers aren't even interested in building?
It's time to roll up your sleeves and get dirty. Here's the fun part!:
- Hire freelancers (via HireACoder, Elance, Craigslist, Mutual Friends, etc) to build the minimal viable product for you. Build something that generates an enticing amount of traffic that will make it easier for you to pitch to potential technical co-founders.
This is great because it will test your capability, self-drive, and willingness to risk something behind this idea of yours. You will learn basic project management, wireframing, and working with technical folks. Good luck!