What's the best, most unforgiving website blocker? I've used StayFocused, but it's too easy for me to just shut off.

I need something that can really, truly block sites for me. Like Reddit, ESPN, etc - let me use them for 45 mins a day total, then shut it down. Or let me shut them down completely for an extended period of time.

Is there anything that won't allow me to cheat?