I bought a brand new Cat Clamp for a song off Craigslist, but haven't put it on yet. It's a bunch of loose cables in place all the way around the Cat. Will be hard for them to saw through cables that MOVE, unlike the solid tailpipes.
Nothing will make it impossible for them to steal it, the idea is to make yours take much longer than an unprotected Cat. So instead of stealing yours, they see how much longer than normal it will take him and move on to the next one instead. There are SO many 2nd and 3rd Gen Runners here.
The cost to replace in CALIFORNIA is CRAZY and I only carry liability insurance to save $$$. I have a garage now, so I sleep much better at night. I was really worried about it for the year I parked it out on the street at night. I know bad areas are of course worse to park it in, but there's SO many stories online about them being stolen at lunchtime in front of stores and hospitals even! Serious jerks!