<?php
header("Location: http://url1.com/\n");
flush();
?>
...and then you are gone.
looks like to some foriegn land where your code does not live and that is the end of the story.
Headers don't work like your idea here.
A header get sent, if there are overlapping directives, the last one is obeyed, that is the law.
Once you tell the browser "Hey my real location is domain-x.com!" that's it, it goes there and doesn't cast a look back.
Consider frames or pop-up windows.
If you are trying to to some weird hit referal cheat-trick, then put a 1pix x 1pix image that links to a script that redirects the image src location to the foreign site.
Since the red x will be too small to see, it shouldn't matter.