I tried Jag's flyswatter but kept breaking them. Maybe the plastic I used is too brittle. Maybe I'm a troll. Anyway...
I added fixed reinforcements to a 95x95mm version. Unfortunately these are not parametric so if you change the grid parameters you will have to adjust them manually (or parametrize them :)). Of course with these it's not flexible at all but anyway with 1.25mm of the PLA I use it wasn't much flexible before that either.
Now it's pretty strong and I can smash these stupid flying things with all the required forces.
2013-08-28 UPDATE: updated scad. parametric reinforcements !