If you're on Mephisto, you'll be happy to know that François Beausoleil just integrated support for Defensio directly into Mephisto... No more plugin to install! While it has not been merged to the official Mephisto repository yet, François invites Rick Olson (author of Mephisto) to do so.
If you can't wait (and I know you can't!), you can just pull from François' Git repository. You'll find the instructions and explanations here.
Thanks for the support, François!