Durable power of attorney

California law presumes people to be competent, unless proven otherwise.  And even if someone is only intermittently incompetent, they are presumed to have been competent at the time of signing any documents.  So what do you have to prove that he is incompetent? A durable power of attorney may not be the proper document that you need to make financial decisions for your dad.  You could also become his conservator.  A conservatorship proceeding is brought in the probate court and a judge has to appoint you as the conservator.  That's better than a durable power of attorney in this situation.