That problem often comes from the contact point between the lockbar face and blade tang being too high. When I first started making folders I thought that it was best to have the whole face of the lockbar contacting the tang. I learned that having a single point of contact down towards the bottom of the tang gives a tighter lockup and reduces the chance of lock rock. If you have an existing knife that you're struggling with, adding a little extra tension to the lock bar spring can help, but probably won't eliminate it.