What's the point of putting a wire in to find the pipe?  Why not just log the path of the trench  and save the file?..in multiple places...maybe even going so far as to export it as a text file and print a hard copy.

I've seen locators tell people lots of stuff that, while technically true, was not really the answer to the question the person thought they were asking.  A log of the actual path is going to stay the same place it was and it is not going to get side tracked on some other old wire or pipe that might be down there.