Even after calling the utility companies and waiting for them to come out and mark the ground, it’s still way too easy to hit unknown utility lines and it happens all the time.  Call811.com explains that calling 811 (this is for the American folks) before you dig, reduces your chance of hitting a utility line to less than 1%.  That may seem like a very small percentage, and it is, but with hundreds of billions of dollars in construction spending each year, that 1% is actually spread across thousands of projects.  This also does not include poorly drawn as-built plans that result in major maintenance and renovation problems down the road due to mismarked and misplaced utilities.