Hate to do it, but...

you know what they say about fences

we bought our house last year, the property line to the south was clearly marked and the house to the north sold a moths later, and they got a survey done, so now all 4 corners are marked
not that you could find them without a machette, there is some dense foliage on those parts (in fact, the surveyers cut a path with machettes but it overgrew again)