Our state doesn't allow local governments to ban billboards outright, even though they deplete value from nearby properties, so all the stuff you have to do to de facto ban billboards leaves you open to litigation.
But there's one option that's guaranteed to work, because it falls comfortably within the city's powers to regulate building materials. If somebody wants to put up a bigass ad, we can make them hand-paint it on the side of a building. Give those art students some jobs!