This worked for me, and quite unintentionally. Dogs learn pretty well if left to their own devices.
While at work one day, the dog, much like yours, found the cord to the answering machine. One problem. It was still plugged in. When I got home, and no power to the answering machine, I checked the plug, found he had chewed right through it. I figured he learned his lesson, and sure enough, he never chewed on another ANYTHING that was "cord-shaped".
Anything you put on it will have to be reapplied whenever it rains, or over a few weeks as it wears off. I know it SEEMS like more work, but burying it would probably be easiest. You don't even have to go that deep with cable. In my area, every cable installer doesn't even plant the cord more than a few inches beneath the surface. Besides, how is it considered "work" if Mrs Stingray does all the heavy work for ya? Haven't you copied out my "Good Wife Rules" for her to memorize?