This plugin allows you to redirect any traffic that finds its way to your development or test site. Under settings, enter the web address for the live production website, check mark the box to activate it, and save. Anyone who comes across your development web address who is not logged in will be redirected to the production website.
Here is the link to the plugin: http://www.tpginc.net/product/tpg-redirect/
You will receive the plugin via e-mail.