Oops! Evidently just taking up a defensive position (however strong-seeming) and staying there doesn't cut the mustard vis-a-vis aliens/weak walls! Lesson learnt...
Let's let our games of Assylum/Reanimator play out, then maybe set something else up.
Actually, since I raced through my later turns in Reanimator (owing to killing off all the zombies on each of my goes), and Impregnator was such a bust, how about you set us up with something before The Assylum has run its course?