The DirecTV boxes have parental software on them, you'll just need to set it up. After you do things over whatever rating you set will just say "blocked title" and require a passcode to view.

Even if you've recorded something on Starz or whatever, that shows a PG movie followed by say PG-14 and you have that extra time period where the original show is over and the next one started already, it won't let you continue viewing the recording until you've entered the passcode.