Personally, if I was Sauron, I would have had a bunch of trolls, orcs, and probably a nazgul standing outside the only damn opening to the only place in the world where the ring could be destroyed. Still, you can nitpick any story, why not just enjoy it?
Yeah, me too. Maybe it didn't occur to him that anyone would try to destroy it as opposed to taking its power for themselves. Seems like a good safeguard though.