There is no such thing as setting it to find "just jewelry", as you say. Gold jewelry is a low conductor. Aluminum is also a low conductor. There's no getting around that. To pass the foil and such, you have to raise the disc. But yes, then you will miss small gold jewelry. If you knock out pulltabs and mid conductors, you will miss medium sized gold jewelry (bigger men's rings, etc...).
Your best bet, if gold jewelry is your goal, is to go where gold jewelry is more prominent, to begin with, especially when compared to the aluminum trash ratio. For example: It is true, that there are gold rings in junky parks. If you dig long enough and hard enough, and dig 1000 aluminum items (I'm talking blighted junky inner-city ghetto parks), you will eventualy find a gold item. But if you simply went to a swimming beach, or volley-ball pits, your ratios go up. The mere fact of people frolicking around while swimming, sunbathing (slippery suntan lotion, cool waters that shrink fingers, taking jewelry off for safe-keeping, etc...) makes the odds better. And digging is easier in the sand.
It also depends on the beach, whether your talking wet or dry sand, whether it's a swimming beach or just a junky fishing beach, whether it's worked to a frazzle already, etc....
