I believe all kinds of technology could be utilized to identify these  but there's little interest. In fact, the Secretaries of State for both Alabama and Florida have an interest in NOT knowing where the old line lays on the ground. Even though it is only a jurisdictional boundary, unfortunately, it has been used as a property description on hundreds of deeds and a change in jurisdiction might cause people to question their land lines.
(concerning the boundary that separates Alabama from Florida: Statute, 41-2-3 of the Alabama Code and Statute 6.08 of the Florida Code.)