THERE ARE NO GUARANTEES
Putting iron on it is no substitute for putting light on it. With light, you know what you are seeing. With just the tip of a probing lance, there is virtually no way to distinguish the encountered object as a utility. It could be a frivolous rock, brick or piece of wood. It could be part of an old concrete slab. It could be anything.
Because probing can involve direct contact with underground utilities, there is the added risk of damage to pipeline coatings.
Probing can also create a false sense of clearance, especially when nothing is encountered below the surface. It is possible to conduct twenty or thirty probes in a 60″ diameter and never detect a 2″ gas line. The probability of this increases dramatically with the depth of the probe. Additionally, how does one distinguish between a quarter-inch fiber optic cable and a root? Guess?
Hydro probing offers no certainty about the presence or absence of underground utilities. The best application of this process is pre-hydro excavation probing, which can be used to spot large diameter structures and utilities prior to hydro excavating to uncover the utility.