Don't mean to make you paranoid but there can be a reason for flying drones over residential areas that isn't about burglary.

It's possible to "hack" people's computers by recording their keyboard strokes (keylogging) by electromagnetic emanations. It's possible to put your set-up in a drone, fly it over people's houses, and pick up and remotely record every key they press on their computers - logins, passwords, everything. The NSA tested it out with success.

Here's a demo:

http://www.securitytube.net/video/215

Although it must be said, I highly doubt that's what was going on. Far more likely that it was just a good old fashioned privacy invasion for a good old fashioned potential burglary.

Ideally, you'd be able to use a jammer to prevent drones from spying on you, but unfortunately jammers are very illegal in Australia - not just phone jammers, but GPS jammers as well. Unlike in most parts of the world, all signal jammers of any kind are illegal in Australia, even for use on private property. Property damage is also illegal - a jammer won't damage anything, but if you throw something at it, that's illegal. Civilians spying on you is illegal, but so is everything you could possibly do to stop it whilst it's happening.

So unfortunately, it's illegal to prevent drones from spying on you.