Unfortunately nothing is theft proof, but I like this idea which I haven't seen mentioned in this thread yet (copied from another site)...
Use carriage bolts to secure a steel plate to the bottom of the generator frame with the nuts down. The plate should extend about two feet beyond the outside of the frame. Position the generator, then park your vehicle with the tire resting on the plate. Keep the muffler in mind when positioning the plate so that it won’t end up pointing at the vehicle. This method of theft prevention is often used by campers
, but could certainly be used at home.
This could be combined with a chain/cable if you're really paranoid.
'04 GMC Sierra 2500HD, CCSB, D/A, MaxBrake, B&W Companion, Retrax Pro, AR Power Steps
2013 Rockwood 8289WS w/Diamond pkg
1969 Camaro RS/SS Convertible
Dad's old 1968 Empi Imp (recently recovered from under 21 years worth of boxes/dust)