Take a chain and test detectors on it.
Then bury the chain in a marked spot and do it again. Vary depth ; and repeat.
When you match estimated conditions of the chain you have inquired about you're ready to practice more. And have the detector you need/want. It is a prior general acceptance that after a hundred hours you will have wrung out a detectors ability. And your own with it.
Most detectors than can locate foil (most reputable ones can) will find a chain IF user is practiced.
IF user is practiced! And patient. And digs mild foil signals.