I have not had this problem (yet) but an ounce of prevention is worth a pound of cure.

My suggestion didn't work... probably what I'll do is rename the admin folder to something else and then when I want to use it, name it the real name and then change it back when I'm done. That's the best solution I can think of right now unless someone comes up with a better one. If someone tries to access mydomain.com/admin they'll keep getting redirected to the main page since it will then technically be a 404 error.