[bmelton]

The advice given pretty much covers it, but the one caveat I'll mention is to try and find a designer whose style you like first.

If you get a bunch of people competing for the work, you can somewhat safeguard yourselves with NDAs, but the more people you bring in, the more likely it'll slip or you'll piss somebody off or they'll think the NDA is over when they don't win the work, or what have you.

While you're perfectly covered legally, your secrecy might well have been blown, and no amount of legal action is going to save that.