Spray them with water or vegetable oil. Water is easiest - just use a high pressure hose to knock them out of the sky / potentially break flight-critical components. Oil requires some special equipment but would presumably ruin the propellers/rotors.
The threat is not in a single one of them, the threat is in drone swarms. We (as in: the general public, I'm quite sure secluded labs have working prototypes) don't have the technical details figured out, but in 5 years, it will be possible for a swarm of 100's of these things to appear out of nowhere (from backpacks, rooftops, garbage cans, sewer drains) and, blitzkrieg style, overwhelm even largish targets within minutes. It will take very sophisticated counter measure technology to correctly identify, isolate and attack a sufficiently large part of such a swarm; technology that will not be available at the time motivated amateurs will be able to deploy such weapons.
Aw, come on. I've got an inanimate bar of tungsten on my desk that's more dangerous than a hypothetical drone swarm. 'Overwhelm largish targets', what, like people are 'overwhelmed' by flocks of pigeons?
If I knew there were 100 veggie-oil cannons on a stadium ready to protect the populace, I'd join a kickstarter campaign to attack that stadium just to see what 100k people covered in oil looks like. I'm equally enthused by the idea of a fire engine following the Prez' car around, or by the Secret Service agents carrying two guns: an Uzi and a water pistol. I do suggest colouring the oil in red, white and blue just for a bit of extra pizzazz.
So the counter measures are more deadly and dangerous than the threat. As usual. One of this combined with red eye detection and a flash could blind a thousand people in a heartbeat.
And what happens when the Prez, PM or Pope is at a rally and 10+ UAVs at the size of small birds start buzzing around? Remember, they are people around, even the sniper has to worry about what his bullet will hit next.
The best, and soon only, good defense against terrorism is a society where people don't want to become terrorists. You guys are thinking in completely wrong terms by worrying about countermeasures. You could create 10 grenade-wielding UAVs, set them for a pre-programmed course above the crowd, out of reach of everyone, and set them off almost immediately. Water cannons, oil cannons or any other countermeasure would be useless. This attack is dirt cheap, incredibly destructive and you don't even need a depressed individual to commit suicide to do it. It could be run from any outside location within a couple of kilometers from the target.
The only long-term solution against terrorism is to just make sure that people's options in society are good enough that they won't resort to blowing things up. This is also the only sustainable way of fighting crime, which any reasonable study will show you.
I'm from Norway, we recently had a terrorist attack that was bigger than 9/11 in relation to our population size. So I'm not saying this as some cold outsider who doesn't see what problems the United States is facing. This is the way things should be handled.
Shame on you sir, for living in advance society, that deals rationally when confronted with a statistically insignificant event of high emotional impact. Shame!!!
On an unrelated note, where can I get your citizenship?
How dare you endanger 200-300 Billion industry with your pleas for sanity. Think of the jobs, think of the political careers, think of the media ... what will the media do if when the next time they call for the president to address the nation because 19 year old set his pants on fire and are laughed out of existence. The current landscape is good at unraveling the social network. But it is oh so profitable.
Not trying to be purposefully antagonistic but water can cause some serious harm when fired out of a high-pressure hose (e.g. the types used in riot "control" situations).
Fly the drone low enough and you have people in the "firing" line.
EDIT - (although, I hope they would realise they do not need the same level of pressure to knock a drone out of the sky. On the other hand, they have the cannons anyway so they might just use those to save having to have a smaller "anti-drone" one.)
Spray them with water or vegetable oil. Water is easiest - just use a high pressure hose to knock them out of the sky / potentially break flight-critical components. Oil requires some special equipment but would presumably ruin the propellers/rotors.