what state are you in?
as many municipalities have maps showing property lines, there are also some for sale APP"S that also show property lines
like this one
https://www.onxmaps.com/hunt-app/fea...property-lines
but keep in mind, most hand held GPS's are NOT very accurate, most have 3+ meter give or take measurements
so unless your working with some very high end surveyor or military grade GPS< your not going to be exact on where property lines are any how!
if you go to your county's property dept, they will have plot maps stating TRUE coordinates on property lines and show where markers are if any!
from there you can go and find them and mark things,
this will also get you exact info on property owners info as well!