Why marking comes before digging
A post hole looks harmless, but it can go straight through a buried gas line, an electrical cable, a water main or a fiber-optic line. The results of a strike range from a cut internet connection to a gas leak, electrical injury or an expensive repair bill that may fall on the person who dug. Underground lines are often shallower than people expect, and the depth can change over time through erosion, grading and earlier landscaping.
Because of the danger, many places legally require you to request marking before excavation, and that includes homeowners digging fence posts. Laws and details vary, so check what applies where you live.
The 811 process in the United States
In the United States, dialing 811 connects you to a regional one-call center, and most states also have a website for requests. The general sequence is:
- Contact the center a few days before you plan to dig. Required notice periods differ by state, and some ask for a minimum of a couple of business days, so do it early rather than on the day.
- Give the details: your address, the location of the work on the property, and the kind of work, such as installing fence posts.
- Wait for the utilities to respond. The center passes the request to member utilities, who send locators to mark the approximate position of their lines.
- Confirm that all utilities have responded before you dig, according to the center’s instructions.
- Dig carefully, respecting the marked areas.
The service itself is generally free to the caller. Other countries have comparable one-call or “dial before you dig” systems under different names, so a quick local search is worthwhile.
What the marks mean
Marked lines are usually shown with paint, flags or stakes. A color code is widely used in North America:
- red for electric
- yellow for gas, oil or other flammable products
- orange for communications, including telephone, cable and fiber
- blue for drinking water
- green for sewer and drain lines
- purple for reclaimed water
- pink for temporary survey marks
- white for the proposed dig area, which you may be asked to outline yourself before locators arrive
The marks show the approximate path. Many jurisdictions define a tolerance zone on either side, often around a couple of feet, within which you should dig only with hand tools or other careful methods. The exact width is set by local rules, so look up yours. Do not assume a mark is exact to the inch.
What public locating does not cover
The free service marks utilities that are members of the system. It generally does not mark lines that belong to you or to a private owner, such as:
- irrigation and sprinkler lines
- landscape lighting wiring
- power to a detached garage, shed, well or pool
- private water, gas or propane lines beyond the meter
- yard drains, septic lines or invisible dog fences
- fiber or cable that a private party installed
For these, review your property records and the installer’s drawings, and consider hiring a private utility locator. Your property survey may show some buried lines or easements, though not all of them. A good survey reading helps, but it is not a substitute for marking.
Digging safely after marking
- Keep the paint. Do not remove flags or marks before the work is done. If rain or foot traffic erases them, request them again.
- Hand dig near marks. Use shovels or a post-hole digger instead of a powered auger within the tolerance zone.
- Move the post. If a line runs through your intended post location, shift the post. Because fence layout is flexible, a few inches or a different spacing is easier than repairing a line.
- Watch for surprises. Warning tape, conduit, sand or a sudden change in soil can indicate a buried line. Stop and reassess.
- Know the limits of the depth. Depth information is generally not guaranteed by the markings.
- Expect an expiration. Marking requests typically stay valid for a limited period, after which you need a new request, particularly if your project is delayed.
If you hit a line
Stop work, and keep everyone away. For a gas line, leave the area immediately and call emergency services and the utility from a safe distance, without using anything that could cause a spark. For electrical lines, do not touch the tool or the ground near it. For water, shut off the supply if you can do so safely, and call the utility. Do not try to repair a damaged line yourself. Report it as local rules require.
How it fits the rest of your planning
Utility marking is one of the first checks in any build and is often a requirement of permits and contracts. If you hire an installer, confirm in writing who requests marking and whether private lines will be located too. It also overlaps with easements, since utilities often run along recorded strips where fences are restricted. Our easements article explains those limits. If your project involves electric gate wiring, trenching a new conduit also needs the same step before you dig.
A free call and a few days’ patience are a small cost against the risks. Even so, marking is not a guarantee, so careful digging remains your responsibility.