iTunes redownloading podcasts

How do I get iTunes to just stop downloading podcast episodes I've already listened to? Literally, I can listen to an episode right now, and then delete it, and the next time iTunes updates, it re-downloads it. And episodes from a year ago. Or three years ago. Or six years ago. It's completely random.

The ONLY way I could think of to at least work around it was to use a smart playlist to only select podcasts that were released within the last week. But the 'release date' is the only field that isn't available to use in the rules. Added date and Modified date are useless because they are the date they were downloaded...which is always today.