Get a few of these and rig them up around the yard.
http://icebearalarm.com/order.html
I've bought a few of these but I have yet to try them out. Thought of connecting one behind the boat etc.
That'll have them chittin themselves running for cover.
The best as mentioned is a load outside siren to let them know they've been detected as well as the neighbours. Although I'm in the country.
I use Dakota Alert 2500 system. I know when something moves in many places in my yard, gate and even a bicycle on my driveway between the gate and road will be picked up. This along with a monitored alarm and another separate remote capability camera system.
They pull onto my driveway, they will already hear my siren from inside there vehicle, so basically "move along" is the plan.