If you really want to be assured of where your boundary lines are then get a professional survey.
We are a fence company, not professional surveyors, even though we do sometimes try to help locate boundary markers for you. But even the markers are not always correct and we cannot be held responsible for putting a fence in the wrong place.
There is no physical feature on your property that is an “absolute” indicator ofwhat is your property which is why we leave it up to you to make sure your fencing is on your property. Don’t rely on old fencing as the legal indicator for your new fencing. For whatever reason that prior fence may not have been built on your legal property line. Even if you are only one inch over your property line you may risk having to tear down a newly constructed fence. Study your house line drawing or order a new survey from a professional.