Bottle Caps

OK, now that I have been reunited with the Musky and hunted an old park and apparent major beer drinking place, I rediscovered the Musky's love for bottle caps. Since there are hundreds if not thousands of bottle caps in the place there must be old coins below this blanket of bottle caps since the park is very old and historic. I have been playing in the yard with surface and buried comparisons trying to find a way to defeat them. With the smaller TS800 coil varying the sweep speed is somewhat effective. But the large TS1000 coil is another story. Has anyone been able to distinguish these from coins?