That's strange, they don't actually have slugs when you create them, so i'm not sure what was being referred to before...
It was just a suggestion...
The above code simply re-directs anyway, there's no reason you have to do it that way...
You could always add this into your page.php, purely an example...
<?php if(is_page('forum')) : ?>
REDIRECT CODE
<?php endif; ?>
It would need to be before the get_header() i think...
There's a number of ways to re-direct (google if you must), but i can't say for definite the above will work, but in theory it should do.... with the necessary re-direct code in place..