What's also kind of pathetic is that... well, I can't believe that the ONLY ryetalyn deposit is in direct vicinity of Flint's mansion. Couldn't they have located a ryetalyn deposit on the other side of the planet, out of his reach? The way Flint describes his robot (M4), it appears to be a single servant ("butler") and guardian. His first one was destroyed by Mr. Spock, and so Flint made another--"Too useful a device to be without, really. I created another", instead of another existing unit of his robot fleet showing up to serve in place of the previous M4. Additionally, with the detected intrusion in the beginning of the episode, you'd expect at least several of these things homing in on the landing party, given the rarity of encroachment. So, Flint clearly doesn't demonstrate the resources to have defensive coverage of the entire planet. If he did, perhaps there would have been an array of robot generation machines strategically placed around the planet, like in TNG's "The Arsenal of Freedom
". Anyway... just a rather easy nit-pick of the episode.