How do you build a secret nuclear bunker? Unless he went into his basement and single handedly dug it out, disposing of the dirt by letting it run out of his trouser leg as he went for walks, there would be numerous construction workers involved who surely would have some inkling that the "wine cellar" they were building was surprisingly well armoured. He could have emulated tyrants from history by killing everyone who worked on it - which I wouldn't put past Zuckerberg, but I can't even dig a hole to plant a tree in my garden without the whole town knowing about it.