A harrow tine sweep is a sensitive item to use as a marker. One horse step and it is turned.
Hidden vaults need little for their hider to locate.
Given the ease with which a septic tank lid can be located after the tank it self is located by a complete stranger to the site by probing ...You're making a lot of work with your imagination regarding any need for markers. Let alone numerous ones..
Post up some of the guns you recovered as locators.
Meanwhile there ain't nothin goin on but the rent. And a harrow tine.
( A harrow tine on a former ag. site? )
The second rule of compass use after never putting one near or on a microwave , is to keep it away from metal objects.
Calm down and sample the alleged vault site.
Excavate all contrasting fill from the adjacent area as in an outhouse dig and take some measurements.
Being you declared concrete the capacity of the wooden pully would be exceeded without much of a vault for weight.
But let's see what you have for a vault first. Not a cistern. Not a privy pit. Not a cellar. Not a silo base.
The why and where of a treasure vault can be discussed later.
Cache valley was aptly named for the numerous cache makers and retrievers.
How many markers are needed to locate an existing cache but not attract anyone else's notice? None is best.
IF you are finding "someone's "locater/sign" , someone messed up!