When I first joined this forum in late 2015, and started reading thru pages and pages of threads, I found out pretty quick that having the Cat stolen was an issue. Since my 4Runner is my only vehicle, and would be a massive, MASSIVE hassle if I was having to deal with replacing the Cat, I decided I'd rather take action BEFORE, rather than after, a theft.
My solution was buying a "Cat Clamp".
Yes, it's overkill. I spray painted the Cat orange, and added my license plate number. I then installed the Cat Clamp and cables. I don't worry about the Cat being stolen. It was funny, tho, when I had the 4Runner smogged, the tech asked if he could take a photo. He was laughing, but I'm sure my T4R is famous within the smogging community.