This 3" or 4.25" pocket holster will absolutely not move out of position in your pocket. The inside is made of a slick pack cloth for a low friction draw, and the core is just the right amount of foam to break up the outline of the gun.
3" holster- fits 2.5" and 3" Derringers
4.25" holster- fits 3.5" and 4.25" Derringers