Hi, tell your son not to give up, i found plenty of not so valuable things. Probably 9 out of 10 signals i got, that i then dug up were trash. But if you keep at it, it does then reveal from time to time something that makes the hobby well worth it.
Peace.
Thank you - we certainly will continue. He's quite excited by his growing collection of random bits of rusty metal......to go along with the stones, fossils and sticks......(that I can't resist bringing home either!).