The problem you get into is that most knife designs are not obviously novel. If you show a knife manufacturer your design and he says, "No thank you," and then comes out with something strikingly similar six months later, you'll probably have a hard time convincing a court that the manufacturer's new knife truly is a knock-off of your design.
As a result, you've pretty much got to get a signed non-disclosure, non-compete agreement. But most knife companies won't sign one for much the same reason: there's not a good way to differentiate designs. They could decide to pass on your design and then come out with something of their own that they totally developed in-house and you could end up persuing them claiming that their new knife is a knock-off of your design and violates the agreements you signed. Because differentiation in knife designs can be very subtile, you may be very well able to convince a court that their new design is illegally-similar to your design, after all, it has a blade which folds into the handle, just like your design. So, most knife manufacturer's aren't willing to sign these agreements.
Benchmade and Spyderco are both known to be honest companies. You can show either Les or Sal your drawings or prototype trusting that they're not going to rip you off.
My advice would be to book a trip to Atlanta for the Bladeshow. Both Les and Sal will be there you can easily talk to both. Major folks from most other knife companies will be there too. The trip may even be tax-deductible as a business expense since you're legitimately going there to try and sell your knife design.