I think the standard is 3 feet deep and if you stick to the standard when your digging it back up you know to start looking at about 2.5 feet deep. If everybody sticks to the standard then everybody knows communication cable is 3 feet deep.So when your hammering in fence posts 2 feet deep and hit a fiber optic cable then you know someone didn't stick to the standard of burring telecommincation cable 3 feet deep.