I used to live in St. Augustine for a few years. I found one of those "once in a lifetime" fields while there. (I'll post pics sometime)
I can't remember the actual directions and I believe it may now be developed but the field (small) was very close to Ponce park and there is a radio station at the end of the road. If you can find what street the radio station was/is on, here's the directions;
Take the street toward the radio station (only one way in as it dead ends at the station) and there is a sharp curve to the right near the waters edge. The field is immediately off the road (on the left) as you enter this final curve toward the radio station.
I found more than a dozen pieces-of-eight/spanish reales, a gold medallion with the name John C. Breckenridge (I later found out he was a VP of the United States, ran for Presidency against Lincoln, was the admiral of the confedaracy and fled to St. Augustine after being pursued out of Cuba ... the medallion had his personal name on front and his street name on the reverse)
I also found OLD jewelry and NO junk, no clad. It was a dream.
FYI - I also hit a location (not as old though) similar to this bonanza in Milan, OH
Anyway, I'm happy to help more if needed.