Assuming the max I/O diff of the 317 is 37V (too lazy to look it up right now)... 37V worth of zeners across the 317--cathode to input, anode to output--would provide some protection against shorts. It's crude but better than nothing. A resistor, fuse or even a small lamp at the 317 input, to limit current under a short condition, ain't a bad idea either. Of course, there are also slightly fancier schemes involving a pass transistor at the input to the regulator, to fix the maximum I/O potential to a safe value.
Does the 317 tend to fail open? (It's been a while since I've had to troubleshoot a PSU that uses one). If so, then there might be some merit to not going out of your way to protect the relatively-cheap regulator, instead letting it act as a fuse for the somewhat more expensive mics :wink: