That's unreal.. someone would actually steal a dish like that. I might think it is someone you know, maybe someone next door, for a prank or somehting stupid like that. Security cam might be a good idea. Make sure they are wired (ethernet or co-ax) as the wifi cams are really easy to jam.
Good luck on the 12 footer, hope that works out for you.
Don't know if you saw it but in Post 3 of this thread I linked to a method Titanium uses to add a security system to a dish. Basically two additional wires are added to the dish that function as a closed loop to an alarm system with a loud siren. When a wire is cut to remove the dish it breaks the circuit and the alarm sounds. Security cameras are great if you have a way to monitor them all the time but this will alarm when the dish is messed with and will likely scare a would-be thief away.