[senko]

Besides a lot of other reasons others already commented about: the noncompete wouldn't prevent that, as Google could hire them for any position that isn't connected to search - say, Android tech support - and allow them the roof access.

You would need to ban them from working ENTIRELY, and no sane person would accept that.

Alternatively, you might realize that NDAs and IP ownership is still a thing, Google can't just copy/paste your code, and if these people are truly irreplaceable, they should either be your cofounders or founding engineers with a significant equity stake.

Not slaves.