DIY
There are numerous anti-theft devices on the market, sold online and in some auto parts stores. These devices hinder the quick removal of catalytic converters, which make them unattractive to thieves. For those with good automotive maintenance and repair skills, you can install your own shield over your catalytic converter.
Likewise, if you can safely access your converter, you may etch your license plate or VIN onto the device, making legitimate resale more difficult.