It's not too bad getting to the fuses, battery is easier being in the boot. The problem with battery disconnection is loss of alarm. As Colin says a visual deterrent is also needed, hence why I use a steering lock. I will just slow them down hopefully.
What ever you do damage is likely if they want the car, we have seen them cutting off locks. In the 80's you would take off the steering wheel or gear stick, but these days with airbags it's a bit risky.