Establishing a power of attorney enables another individual to make decisions on your behalf. Depending on the specifics of your unique concerns, a power of attorney can be tailored to particular situations, such as when you become incapacitated or can exist from the moment that it is signed.
Revoking a power of attorney raises unique legal questions. Many people who have established a power of attorney might be curious about whether or not they can set up a power of attorney and ultimately take it back in the future, particularly if they no longer trust the individual who is established as the agent or if that person no longer wants to serve. 
A power of attorney document can be revoked if the principal executes a written document identifying the power of attorney and requesting that it be revoked. The attorney in fact or agent who has been established with the power of attorney also must receive actual knowledge about the revocation. Until he or she gets that actual knowledge, the revocation does not become effective.
Sending the revocation letter via certified mail with return receipt requested is strongly recommended and it is a good idea to follow up and ask whether or not a power of attorney revocation has been received by the agent. This information is important for carrying out the full revocation of a power of attorney and verifying that you are eligible to establish a new power of attorney as soon as possible.