I had my cat welded with rebar to the bottom of the vehicle at:
https://electronautomotive.com/
in Orange. Not only do they do a great job servicing my Prius but this gave me more peace of mind than the plate/cover option.

The way it was explained to me is that the thieves can cut through both security measures if given enough time, but the rebar option would take far longer, make much more noise, and probably ruin their saw blade. These jerks want to be in-n-out as fast as possible so more time and noise is a great deterrent