A crazy thought for desperate times: if you park on the street, roll down the rear window and tape a plastic bag over the opening before leaving. Other people may think: 'poor guy already got broken into and had to cover it with plastic.' Thieves may think: 'easier to pull that off than break a different window.' Who knows?
Based on the stories I hear from friends and co-workers, plus the amount of auto glass I've seen in parking lots, I don't think the problem has gotten significantly better in the South Bay. Haven't had my window smashed again since removing the parcel shelf, though.