Barnett, J. P., & Burton, J. D. (1997). Osage-orange: A pioneering stewardship species. Tree Planters’ Notes. (Link to PDF)
This fence post study was reported on in 1996 after the posts had been in the ground for 66 years. All of the untreated osage orange fence posts were still sound in 2016 after 86+ years in the ground (Jeff Morrell, original author, personal communication, February 2016). No other species, treated or untreated, had any remaining posts over this time.