What if someone hired even more private security, and just tore the whole thing down? What if they shook everyone down, took everything and bailed? Is this a 'perfectly anarchist response'?
It's a good response, and it proves that "hiring security" is not anarchist at all. Anarchy is about preventing power concentration, quite the opposite of guarding by force.
Where do you get the power to prevent power concentration?
You agree on rules in which accumulation is impossible, or naturally short-lasting.