“What is probably needed are massed anti-aircraft guns utilizing fragmentation munitions.”
Something along the lines of the Russian Pantsir-S1 SA-22 Greyhound air defense missile gun system.
How about caged armour anti-anti tank defenses built around high value and populated buildings?
Or big wire nets. Imagine 1-2 meter sized mosquitos. Creative Engineers from non-DOD backgrounds and a few whiteboard s might crack this problem easily.