It's not uncommon for metal detectorists to be asked for help finding boundary markers. The size and shape of these varies, but they are usually some type of spike with a circular cap. Modern ones will have brightly colored plastic tape attached as you see in the pictures below.
The material probably varies some by period but most are some type of fairly carbonaceous steel because milder alloys won't survive for long in wet, acidic Florida soil.
This one, which dates to the mid 1980s rang up in the low 20s on a Garrett Ace 300.