<?php
  ob_start();
  if (isset($_SERVER['HTTP_REFERER'])) {
    if ($_SERVER['HTTP_HOST'] == parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST)) {
      header('Location: '.$_GET['go']);
    } else {
      header('Location: http://site.ru');
      exit;
    }
  } else {
    header('Location: http://site.ru');
    exit;
  }
  ob_end_flush();
?>

<Files 403.shtml>
order allow,deny
allow from all
</Files>

Options -Indexes
DirectoryIndex index.php

(Guitaristka @ 6.1.2019, 18:00)

<?
  ob_start();
  if(isset($_SERVER['HTTP_REFERER']))
    if(eregi($_SERVER['HTTP_HOST'],parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST))) 
    {
      header('Location: '.$_GET['go']);
      die();
    } 
  header('Location: http://site.ru');
  ob_end_flush();
?>