I have one that I had an attorney draw up giving my daughter power of attorney. It hasn't been filed with the court but all my daughter has to do is take it to the district court and file it if I become incompetent. As far as I know, once it is filed it can't be undone. Since I am competent at this point he said there was no reason to file. I also made her executor of my estate. My husband is not real happy about it but since she inherits everything I have (which was mostly inherited from my parents), I thought she needed to be in charge.

I think probably every state is different, so you might want to consult an attorney if it's really important to you.