Vows of secrecy

The details for this weekend's wedding of Lachlan Murdoch, son of media tycoon Rupert, and supermodel bride-to-be Sarah O'Hare are under tight wraps.

Guests have been sworn to a confidentiality agreement and the planned location of the big event is still a secret.

But the word is it will be at Cavan, the Murdoch estate at Yass, near Canberra.

It is expected Lachlan's guests will gather tonight on his father's yacht in Sydney Harbour to wave farewell to his bachelorhood.