I'm currently using this plugin https://nl.wordpress.org/plugins/rename-wp-login/ to change the login url for my websites. It's really a small plugin with just a few lines of code.
I think it would be a great feature to add to your WP Defender plugin. Since the main reason i'm using this plugin is safety. But yet another reason is for me to show my customers a nice login url instead of 'wp-login.php'.
Since I dream of a world where I only use wpmudev plugins, I'd love to see this feature added to WP Defender plugin (which is already awesome).