Marking the latest effort by celebrities to erect a wall of privacy around their personal affairs, it was disclosed on Wednesday that teen singing star Justin Bieber is requiring guests at his home to sign a non-disclosure agreement barring them from discussing details about their visits via any media whatsoever. The NDA was revealed by the tabloid website TMZ, which has frequently reported in the past about the goings-on at Bieber's parties held at his Calabasas, CA mansion.In what today's New York Daily News called a keep-quiet-or-pay-me waiver form, the NDA states, [Since] it would be extremely difficult, if not impossible, to ascertain the monetary damages that would be caused by your breach of the terms ... [you] therefore agree that any breach of [the] foregoing confidentiality provisions shall be compensated by a payment of Five Million Dollars. Several publications (even China's state-run Xinhua news service) noted that such documents are fairly commonplace in Hollywood, and New York magazine's celebrity website remarked, If you think it over for a second, this is perfectly reasonable. It is even -- dare we say it? -- legally responsible. He's Justin Bieber! He can't just be letting random strangers into his home and then allowing them to sell weird stories to tabloids.