Whenever you dig in your yard you should be aware of the attendant hazards of buried utility lines.
There is a free service for homeowners available. The Utilities Protection Center, funded by all the utilities such as gas, cable, telephone, etc, will send someone out to mark all the utility lines and pipes on a property.
They may be reached at 770-623-4344 for metro Atlanta or 800-282-7411 for statewide service. All they ask is three working days notice.