Robbers are a) motivated by prior intelligence from 'robber scouts', and b) focussed on smell. So - wet sheets and panes of glass are a waste of time.
The best solution is anti-robbing mesh over the entrance, which really needs to be in place from the outset to outwit the robber scouts. It's great fun watching potential robbers unable to figure out how to break in, while the residents simply walk around the side of the mesh, effortlessly. But - if instead, word gets back to the 'robber hive' that there's easy pickings to be had, the situation can very quickly get out of control - as you've found out.
One way of stopping robbing in it's tracks is to fully seal the nuc entrance for 24hrs - but that requires a nuc fitted with some means of adequate ventilation.
Perhaps the best solution of all is something I'm working on at this very moment: to create nucs - not by splits or shake-outs which creates small, vulnerable colonies - but to create nucs over a parent hive, which should then generate a fully functional nucleus colony, complete with it's own workers, foragers, and most importantly - it's own mature guards. I'll post more about this when I've finished the trials I'm currently running - providing they're successful, of course.