Do you know how deeply the cable is buried? Can the electric (or whatever) company come out & mark its location for you? They can probably tell you if it's down far enough to be/not be a problem.

Just a suggestion--would it be possible to avoid the cable issue altogether by planting in containers instead of in the ground?

Re: digging up the lawn--hmm... if you can loosen part of it somewhere away from the cable, maybe one of those small 3-prong forks would work from there. Don't know.

If you *do* get the lawn dug up, another suggestion is to plant seeds (rather than plants) directly in the soil. If you start from seeds, you won't have to dig deeply, and I can't imagine the roots of annuals would become so thick/strong as to be a problem in themselves.

Good luck!

Stacy already gave wonderful advice. Suggestion, use the lasagna method to bury the lawn, (I hate grass), put weedblock and gravel on top, and plant in decorative containers or a raised garden. Put the containers on top of slate or bricks or concrete blocks or anything you enjoy. I use concrete blocks. Why have grass when you can have flowers, including evergreens? I know,it's a personal taste issue, and I hate lawns.