This video shows my practice of layered simulations and displaced interior of rocks.
For the simulations part, the key is to keep the animation from the low-res simulation and activate the second part of detail debris. The purpose of using this method is to keep the layout of the large pieces maybe approved by the director. There's no constrain needed in the second part simulation.
For the displacement part, the purpose is to add the interior detail from SHOP level instead of using hi-res model in SOP. Artist can add infinite detail when rendering. The key to achive this is to storing the rest position data and transform matrix for rotation.