Untested. This hook will only allow access to ACP if the IP Geolocation matches a defined value. Only works with CloudFlare.

hook_cf_country_admin

<?php
/**
 * hook_cf_country_admin
 *
 * This hook will only allow access to ACP if the IP Geolocation matches a defined value. Only works with CloudFlare.
 *
 * @author		k0nsl (http://k0nsl.org)
 * @link		http://k0nsl.org
 */
 
/**
 * @ignore
 */
if (!defined('IN_PHPBB'))
{
   exit;
}
 
/**
 * allow only access if HTTP_CF_IPCOUNTRY matches the value in array, if it doesn't we pour out a cryptic message and redirect
 */
function hook_cf_country_admin(&$hook)
{
$req_uri = $_SERVER['REQUEST_URI'];
$reg_pattern = '/adm/';
if (preg_match($reg_pattern, $req_uri)) {
  if ( !isset($_SERVER["HTTP_CF_IPCOUNTRY"]) )
    return;
 
    if ( !in_array($_SERVER["HTTP_CF_IPCOUNTRY"], array('DK')) )
    {
                $urel = 'http://k0nsl.org';
                echo 'Sorry, but you cannot login at this time.';
                header("Refresh: 5; url='.$urlel.'");
                exit;
    }
}
}
 
/**
 * initialize the hook
 */
   $phpbb_hook->register(array('template', 'display'), 'hook_cf_country_admin');
?>