Add http(s) to URL if it’s not there?

Use a before filter to add it if it is not there:

before_validation :smart_add_url_protocol

protected

def smart_add_url_protocol
  unless url[/\Ahttp:\/\//] || url[/\Ahttps:\/\//]
    self.url = "http://#{url}"
  end
end

Leave the validation you have in, that way if they make a typo they can correct the protocol.