Hundreds of model helicopters flying in sequence can stop a military air craft!
How you might ask?
If each of the hundred models carried a small chrome molly ball of say 3mm diameter and the aircraft flew threw the curtain of models then there would be a catastrophic failure if the jets engines caused by these small balls.
For a cost of say $10,000 a city could protect it's self from the ravages of marauding aircraft bent on destruction.
The technology is there already all that is needed is application.
Watch this space for up and coming news of these defensive weapons.