Drone defense is very interesting....but I find the concept of jamming/electronic spoofing/RF commandeering somewhat comical in this arena. (what ApolloShield seems to be doing)

This is a physical threat (in the terrorist scenario) that needs to be dealt with kinetically.

RF spoofing doesn't work for planed flights, GPS spoofing can work but reply attacks are wonky at best and most just will trigger a "go home" which is easily overridden to be the target.

Skywall (http://openworksengineering.com/skywall) type stuff is interesting, but very hard to get right...know a few folks in the field working on some cool stuff.

The passive whoops I'm a terrible drone pilot and flew my drone over moffet is fairly easy to deal with (betting we'll see some sort of drone tagging (RF)/mgmt system tied to the in-place registration very soon)...but not nearly as lucrative as true airspace security

/2cents from someone not in the field but interested in it