Play hardball then. Set a passcode that only you know then go in the controls and set everything to the lowest settings so it requires a password to go to every channel. When you want to watch then you turn it off for yourself and THEY can watch YOUR shows with you. Tell them you'll unlock the gates to the TV once they agree to not do what you're telling them not to.
I'm obviously being sarcastic...but maybe you could try that for a couple of days?! Unless you wouldn't get a good night's sleep on the couch.
Good luck with all that!
<For the new and reruns setting, while I sat down with my wife and showed her the do's and don't's on the new DVRs as we got them (and she's great at it now), there are times where she rushes or the Hopper freaks out and the record option gets set to new and reruns by mistake, which is a pain.>