NAT?

Look at how the FT has implemented it. Old pages do not have access and new pages allow users to have access. Is FT secure? I would say that yes, getting old content is almost impossible.
Making it available to Google (News) is not the same as making it available to the whole world. Google does not cache the pages, so you have control of what your users see.
As an administrator, I advocate: Give the choice to the administrator of the web site.

BTW I have tried implementing this in the and so far I have not had any success:
ip_acess, returns an array of the ip address and the user related to that address (to control permissions)

 function user_access($string, $account = NULL) {
  global $user;
  static $perm = array();

  // User #1 has all priveleges:
  if ($user->uid == 1) {
    return 1;
  }

  $ipok = ip_access ($string);
  if (is_null($account) && !$ipok) {
    $account = $user;
  } else if  ($ipok) {
	  $account = $ipok;
	  };

  // To reduce the number of SQL queries, we cache the user's permissions
  // in a static variable.
  if (!isset($perm[$account->uid])) {
    $result = db_query('SELECT DISTINCT(p.perm) FROM {role} r INNER JOIN {permission} p ON p.rid = r.rid INNER JOIN {users_roles} ur ON ur.rid = r.rid WHERE ur.uid = %d', $account->uid);

    while ($row = db_fetch_object($result)) {
      $perm[$account->uid] .= "$row->perm, ";
    }
  }

  return strstr($perm[$account->uid], "$string, ");
}

Since I do not have a spider, I have tested this though a php page that fetches my web site into a variable and displays it. My php page displays:
warning: file_get_contents(http://www.info-europa.com/clientarea//?q=node/330): failed to open stream: HTTP request failed! HTTP/1.1 403 Forbidden
in /var/www/html/clientarea/test.php on line 15.

Look at how the FT has implemented it. Old pages do not have access and new pages allow users to have access. Is FT secure? I would say that yes, getting old content is almost impossible.
Making it available to Google (News) is not the same as making it available to the whole world. Google does not cache the pages, so you have control of what your users see.
As an administrator, I advocate: Give the choice to the administrator of the web site.

BTW I have tried implementing this in the and so far I have not had any success:
ip_acess, returns an array of the ip address and the user related to that address (to control permissions)

 function user_access($string, $account = NULL) {
  global $user;
  static $perm = array();

  // User #1 has all priveleges:
  if ($user->uid == 1) {
    return 1;
  }

  $ipok = ip_access ($string);
  if (is_null($account) && !$ipok) {
    $account = $user;
  } else if  ($ipok) {
	  $account = $ipok;
	  };

  // To reduce the number of SQL queries, we cache the user's permissions
  // in a static variable.
  if (!isset($perm[$account->uid])) {
    $result = db_query('SELECT DISTINCT(p.perm) FROM {role} r INNER JOIN {permission} p ON p.rid = r.rid INNER JOIN {users_roles} ur ON ur.rid = r.rid WHERE ur.uid = %d', $account->uid);

    while ($row = db_fetch_object($result)) {
      $perm[$account->uid] .= "$row->perm, ";
    }
  }

  return strstr($perm[$account->uid], "$string, ");
}

Since I do not have a spider, I have tested this though a php page that fetches my web site into a variable and displays it. My php page displays:
warning: file_get_contents(): failed to open stream: HTTP request failed! HTTP/1.1 403 Forbidden
in /var/www/html/clientarea/test.php on line 15.