A lot of people are under the impression that PI's only find lots of iron, bobby pins, other metallic junk and with some luck....a ring. That is simply a myth. Using the iron check, the audio tones (you have to learn them), the swing width, the 8 quiet blips on most bobby pins and straight nails and the roughness sound on many bottle caps vs. a coin, allows the user to actually leave a lot of junk in the ground. Between learning your PI detector well and choosing proper locations to use a PI, you should be able to get a nice batch of coins in the water or land. If you are looking for old silver and old copper coins, dig only the low-high signals instead of the high-low signals. The modulated audio also allows the user to just dig the deep targets.
These coins were found in during my learning curve, for the first 8 water hunts. I averaged about 50:50 ratio of junk vs. coins & jewelry. That really is pretty good, considering some water hunters dig it all, no matter which brand/type of metal detector they use.