your wife better call her company's insurer unless her business involves dirt work now. As soon as you start digging, your insurance goes up. Lots of buried things that cost $$$$$$ if you cut them... think fiber optics
The KTAC insurance policy would cover the tractor itself in the US and Canada, but for what you are wanting to do you would need a good Liabilty Policy in case you hit something.
As a word of advice, always call the Utility Locator people several days in advance (it's a free service here in NC) and have them come out and mark the underground utilities, that way if you hit a buried line they didn't mark you won't have to pay for it.
Fiber Optic = Probably the most expensive cable you could ever cut.