Michael Fellows was right about the extra piling used by Roger Bullivant (NCE 27 April) but there is a quicker and cheaper locating method than the one he suggests.
Since working on pipelines in the late ties I have found that two bent reinforcing bars held loosely, one in each hand, is amply effective for nding all manner of below ground services. Probably best of all, and to the amazement of client and contractors alike, was nding a water main 6m under a metalled road using two coat hangers - but I now keep handy a purpose-made set of bent rods with loose handles purchased for £4 in 1990 and, I see, still available on eBay for £5.70.
Gordon Rose (F), ROSECHARLBERT@aol. com