To add onto David's explanation...
To defeat a rolling lock or axis lock, you need to shear a metal pin, or collapse the frame while trying. This is very very difficult to do, and these lockups are incredibly strong. I can tell you from experience that holding a rolling lock knife, it feels like a fixed blade, there is no flex anywhere. Both lock types should be difficult to unlock accidently. The springs that both locks use to couple to their unlocking levers used to be a concern, but any problems here seem to be solved.
The liner lock and Sebenza-style integral lock both work by blocking the back of the tang. Since the integral lock moves the entire handle side over, the entire tang is blocked by a massive amount of metal that is unlikely to slip off. It is very strong.
The liner lock moves the liner behind the tang, and the liner is usually significantly less wide than the tang itself. It is not as strong as the integral based on the amount of metal blocking the tang. Done right, this format *is* plenty strong for just about any use. But very few companies or custom makers do it right every time. Ironically, I'm in the midst of an email conversation with a guy whose Microtech closed up on him, causing many stitches. If the best production company can't do it right every time, that's cause for worry.
Most people end up using their tactical folders for opening envelopes and boxes. Those people won't find problems with their linerlocks, because they barely even use the lock; if that's you, have no fear of liner locks. But put some stress on the spine and it's a different story. I can often easily pop the locks on the knives of guys who claim liner locks have no safety problems. I've done this so many times that I believe now that they're just not looking hard enough (or don't know how to look)!
The lockback, by contrast, is a lock that's easy to do consistently well, and when done so is good and strong, about as strong as a liner lock. It usually doesn't open as smoothly as the above locks, but there are some rare exceptions. The main concern is placement of the unlocking tab; put in the wrong place, the palm can accidently spring it. Also, if too much pressure is placed on the blade, the tooth on the spring can pop out of the blade-cutout, and the knife will close. Probably not something most people will see in a strong lockback though.
Overall, it's no coincidence that many of us who own many lockbacks and liner locks are desperately looking for some relief, some lock type that we can trust a bit more. The integral lock has proven to be a better mousetrap, the rolling lock looks like it might be better still, and the Axis lock holds just as much promise.
[This message has been edited by Joe Talmadge (edited 08 December 1998).]