I request clients mark their own sprinkler heads before I will aerate....... Client tells me today their service guy will not be powering up system till May. So is there a secret to locating all heads before they are activated? Yes they should have a map!!! But we know that ain't the case. Any tricks for finding secreted heads. I do not know if they have any metal.... would a metal detector work? It's OK to tell me if this is a stupid question.