Idea for Countering Anticrowd Microwave Guns

It might be possible to foil the microwave anticrowd weapon by sandwiching heavy layers (or perhaps several) of aluminum foil between cardboard signs, carried by most or all members of a demonstrating crowd.  When attacked by the weapon, the front rank of the crowd holds large signs protecting the crowd, while the rest of the crowd holds its signs so that each one faces the source of the microwaves.  This should fling much of the device's output directly back at it, perhaps damaging or destroying it, or possibly inducing its operators to desist, either in fear for the device or to avoid discomfort themselves.