A mechanism and method is provided for preventing instantaneous unlatching of a driving and a driven member upon an accidental drop in the hydraulic-holding pressure. One embodiment of the mechanism includes a housing having an inlet port connectable to a substantially sustained high pressure fluid source; and a configured locking pin axially displaceable to an engaged position with respect to the inlet port in response to high pressure fluid entrapped in the housing. The locking pin is spring-biasingly axially displaceable to a disengaged position when the pressure is low. The axial displacement of the locking pin sufficiently overlaps the inlet port to form a variable orifice so that the rate of exhausting of entrapped fluid is variable. In another embodiment, the entrapped fluid is slowly exhausted until a seal length is reduced to zero by the retraction of the locking pin. In another embodiment, latching and unlatching is controlled by pressure pulses. In the latched state, contact between positively-engaged parts negates the need for sustained high fluid pressures.