A radio in a 4runner is hell to rip out. it's isomounted. even if you smash the dash, you need at least 6 screws to tear it out. Way too much hassle for a thief.
Definitely true for the original factory mount but aftermarket mounts and adapters aren't necessarily as robust. For example, my cheap plastic single-DIN adapter came from Crutchfield and it attaches to the dash frame using only two screws. Even if it had more screw holes, it's flimsy enough that I suspect a thief could just break it loose rather than bother with the screws. I probably should have spent more time trying to make the OEM metal bracket work.
Does anybody make a more robust metal single-DIN adapter that fits an 06 4R?