The best reason to set up a power of attorney for yourself or an elderly family member is to avoid a far more contentious and expensive alternative later: guardianship. A power of attorney becomes urgent if an elderly family member is showing early signs of dementia. “You want to run, not walk, to get that done because capacity tends not to get better,” said Jonathan Williams, an attorney with the Clarity Legal Group in the Raleigh-Durham, N.C., area. “Having good legal documents in place, if the person has the ability to execute them, can be helpful later on,” he said. In a power of attorney, the person signing the document agrees to name an agent, usually a trusted family member…