A locking device prevents stressing of other components used to hold tool portions against relative movement until a desired location is reached. A locking dog holds a first component, such as a sliding sleeve to a second component, such as a mandrel until pressure can move a piston and remove support for the dog. The same pressure that removes support for the dog to unlock the lock also forces a retainer, such as a shear pin that holds a sleeve to break to allow the sleeve to shift. The locking dog keeps stress off the shear pin when the locking dog is supported in the run in configuration. An alternative design uses a grease filled cavity to dampen shocks that could load a shear pin to the point of failure.