Hi mm43,
The only purpose of my comment was to remember it is possible to locate buried ferrous and also other metals with simple devices.
The "oscillating tuned circuit" being moved to nearby not visible metal objects is a simple solution. There are other approaches.
The rationale is: A metal (ferrous or not) changes the environment of a coil and this can be detected. How? Can be by the voltage at coil terminals. This is used in aviation, the "Eddy current tester" for metal checking.
I must study if at salt water, high pressure and salt sand burying a small aluminum (Dural, Avional, Hiduminium) part; To check if the issue is more complex at this environment.
My intention was not to correct you with the bold red. Was to remember we are able to locate not just ferrous.
On the IC memories (non volatile) i commented just to remember the magnetic fields generated by locators will not affect recorded data.
Stay sure my comment was to ADD and in an assertive way communicate to clarify inform what i am convinced.
Sometimes we can fail and learn from errors. With a good and constructive intention this can be just a small CAT (clear air turbulence) in our "learning route". To further reduce the "error rate".