One practice we have done in construction for buried cables or conduit was to lay one of those red or yellow ‘caution’ tapes in the trench just below the surface during the backfilling of the trench after the runs are installed. This way, many years later if you dig, you’ll be alerted by the tape and know that if you go deeper, you`ll find the conduit or buried cable. An advance warning system…Better to cut the tape by mistake with the shovel than the wire run!