Been using spyderco lockbacks pretty much daily for the last 15 years, mostly a first generation Endura. They're quite possibly the most reliable lock I've ever used, this means Axis, button, axial, frame, and linerlocks from microtech, benchmade, spyderco, US made Camillus, Buck, etc. Linerlocks in particular have a tendency to be difficult to make right, or tend to unlock themselves during "hard use" due to design issues. You CAN make a spyderco midlock (and pretty much any lock) fold if you know some tricks, but it's been my experience that unless you try on purpose it's not going to happen in real world use. The endura 4 has a Boye detent, the small round cutout on the exposed lock bar that makes doing this even more unlikely than with my first generation endura.