[bdg]

Something as basic as a wire mesh would fit the bill.

[andygates]

It probably wouldn't, when the rotor has incredible suction and the tangle wire is very thin. I would certainly expect an attacker using monofilament and a defender using several-mm mesh to go the way of the attacker. Too much protection and you lose the airflow.

I must immediately tape speaker mesh to my AR drone! FOR SCIENCE!