Plastic Drain Pipe Locators?

[flusher]

I have recently placed 3ea 250ft plastic drain tiles at 3-4ft depth in a field to help move excess water away during late Fall to early Spring. At the moment I can still see where I laid the tiles and have noted them on blueprints. But to be honest there is not much accuracy in the notation. I'm thinking about using a small section of cast iron pipe at the beginning and end of the tile run at 3ft depth with the idea that I can use a metal locator like those from Schonstedt ... Schonstedt Instrument Company : Magnetic Locators, Pipe and Cable Locators to locate the run?page=indexml&gclid=CIWp2aOIsqoCFQXc4Aod60AB7g . These are rented locally for not much money. Anybody have experience with subsoil metal locators? How small can the object be and at what depths? .....Thank you, Gary

Putting iron in the trench is a good idea.
I prefer to lay an insulated copper wire in the trench with one or both ends left above ground. When you want to find the pipe, connect the end of the wire to a tone generator (oscillator) and use the equivalent of a metal detector.