How can external linking be managed effectively in PHP projects?

External linking in PHP projects can be managed effectively by using relative URLs instead of absolute URLs. This ensures that links will work correctly regardless of the project's location or domain. By using PHP functions like `dirname(__FILE__)` or `$_SERVER['DOCUMENT_ROOT']`, you can dynamically generate the correct path to external resources.

<a href="<?php echo dirname(__FILE__) ?>/external_page.php">External Page</a>