I know that he did not think that anyone would want to destroy it, but rather that somebody would instead claim it and try to fight Him with it, but if there is only one place on the planet where the Ring can be destroyed, and the Ring means so much, and you are at active war, and you hear tidings of "Isildur's bane" and of Elfish warriors and spies sighted in the heart of Mordor, why not at least appoint one lousy orc or perhaps a couple of Watcher statues that keep everyone away from that place which is the last that Sauron would want anyone to go near if they indeed have the Ring, whether or not they know how to destroy it and have intended for this to happen?
It's possible that it could be destroyed by accident, for example if somebody claims it and then marches toward the Dark Lord's main lair, which, as I understand it, is very close to the Mount Doom.
It seems to me as if Sauron is very foolish in this specific regard, but very calculating and clever in all other ways. I just don't really understand why. Why leave the possibility open? They were two very weak, half-dead hobbits, and they also had Gollum lurking around. The slightest guard could have stopped them from ever entering, and even if they didn't, like how the Watchers failed, at least it would have shown that he had thought of this, however unlikely he deemed it.
