Avoiding caching PHP pages:
After lot of tries and research this is the best combination of headers I've found that seems to work well even with the proxy of visitors that are using satellit connection.
<?
header("ETag: PUB" . time());
header("Last-Modified: " . gmdate("D, d M Y H:i:s", time()-10) . " GMT");
header("Expires: " . gmdate("D, d M Y H:i:s", time() + 5) . " GMT");
header("Pragma: no-cache");
header("Cache-Control: max-age=1, s-maxage=1, no-cache, must-revalidate");
session_cache_limiter("nocache");
?>