A General Power of Attorney may be revoked by either the principal or the attorney-in-fact (the agent). A general power of attorney is also terminated if the principal dies or becomes incompetent.
A Durable Power of Attorney is specifically designed to continue to be effective even after the principal becomes mentally incompetent. Frequently husbands and wives grant Durable Powers of Attorney to each other, so that when one becomes incapable of making financial decisions, the healthier spouse can act as attorney-in-fact to execute documents and make financial decisions.
Another variation of the durable agency relationship is the Durable Power of Attorney for Health Care.