The larger the shock the greater the FI's exposure. The FI manager must adjust his leverage adjusted duration gap to immunise against interest rate risk. As an alternative the use of derivatives in conjunction with balance sheet manipulations is a better option. Duration also changes as time passes and also at a different rate to real or calendar time. After one year duration may have changed to say 4.31 years instead of the 4 required.
Bond therefore needs to be restructured.
Options could be to sell a portion of the bonds and replace them with some of a shorter duration. This indicates that constant adjustment is necessary to maintain your position however from a practical point of view reviews should only be done at intervals eg. 1bp however has substantial deficiencies when larger changes occur. Duration overpredicts the fall in values for large rate increases and the rise when large rate reductions occur. This property is called convexity rather than linearity as assumed by the basic duration model.