This video from Germany (I think) is showing robber bees crowding in through a little hole above the regular entrance. It also shows a really simple way to attach hardware cloth mouse guards using push pins.
I did a spot inspection today and my bees were robbing like mad. Trying to anyway. Every hive I checked still has at least some brood – in one I even saw quite a few eggs. But they all seem to be well stocked up for winter – so I’m finished feeding sugar syrup for the year.