this thread is ridiculous.
to guard a generator in your yard- use your cell phone. when crimes happen that don't threaten your life you've already paid for someone else to handle that for you.
Their number is 911.
The alternative? Get some protection in case someone steals your generator and you follow absurd advice to shoot over it. I'd suggest (again) your cell phone. Program the number of a few good attorneys in.... you'll need it.
Alternative #2: big dog.
During / after a hurricane phones may not be working, not to mention police have more important things to do than worry about someone stealing gas or even a generator.
Dog & chain work. I doubt someone is going to come in my yard to steal my generator with me home. I have neighbors nearby also...
If they are a real threat then I don't want rock salt shells.