It all just depends on what public property it is, and how well it's been hit. In my area: Even some of the private property sites (stage stops, defunct picnic grounds, etc...) have been hammered to death too. So ... it just depends. It's also a regional thing: In some parts of the western states, the yester-year md'ing pressure was apparently light . Because I am shocked to find that some of the places (even public) that we try, have had very little pressure. Versus my area, which has had brazen hard-core guys, who hit the history books, decades ago.
Become a member , and docent/volunteer at your local historical societies and historical museums. Usually requires 6 hrs. (or whatever) time per month. Doing things like manning a desk, sorting papers, etc... And it gives you a name badge and title. For example: I lead 4th graders through tours at one of the CA missions. So I have the docent badge on a lanyard. At another museum, I man a desk (greet visitors) a time or two per month. Which affords me another badge.
By having those "credentials", it helps break-the-ice better when talking to private land owners. Eg.: "Hi, I'm a worker at such & such museum. I'm doing research for an article I'm writing on such & such. Can I ask about the stage stop that was said to be on the back-40 of your property in that canyon over there ?" And then slowly morph it into permission to go take some pictures. And then morph to md'ing, etc....
Also: Cold calls on the phone, and cold call emails RARELY work. Because, of course, they do the same thing you and I do with junk mail and door knocks from total strangers: Hang up, and turn-away door-to-door solicitors. Instead: Find some way to "catch them on their front porch". I've even staked out gate locations, at probable times when persons would be coming home from work, *just* to "bump into them" and start up small talk.
