a boundary marker is not a pin placed for an individual survey.

around my area a boundary marker is generally only found in a units of division no smaller than a quarter section (160 acres).

These are used by surveyors for starting points in locating a particular plat of land. To the average person, they are basically useless in determining property lines.

Sometimes boundary markers are things such as trees and piles of rocks so they do get displaced occassionally and need to be reset.