Yup, Larry is right: Any machine can find low conductor gold rings. All you do is turn down the disc
Sure, some are better at low conductors than others, but that is HARDLY the "problem" in the typical sports fields and parks. You will typically NOT LACK for "low conductors" to choose from, if/when you simply lower your disc. on any machine, and go to the average city park turf.
Now ...... if the discussion were about earing studs, dangly tinsel thin fine chains, etc... then yes, certain machines can find those, while the typical "power-house" machine will miss grain of rice and tinsel fine objects. But if you're going into park turf in a quest to find objects that dainty, you're going to be one-sorry-fellow indeed. You will quickly learn how punishing it will be to think you can go to the average city park, and think you're going to strip-mine out every staple, push-pin, BB, etc.... At a certain point, you'd have to ask yourself: "why am I hunting for objects this small, in this type environment?". If those things were your goal, you're much better served going to swimming beaches and/or sandbox type environments. THEN there are certain types of machines which can find dangly chains better. Heck, to be honest with you, swimming beaches are also better for rings (verses park turf) as well.
But for regular park hunting, for regular rings (even small foil-reading type gold rings), then ANY machine will do it, when you turn down your disc.