If it's a historic site like that, chances are it's already been hunted more than once. Usually the high tones are gone, and the lower conductors are left. They're still goodies. I always concentrate on the front yard, that's where most of the activity was. I commonly dig Indian cents near the road, folks and kids would sit and watch the travelers pass on by.
I'm pretty sure this actually is the case. Thinking about it, my grandmother would have given permission if the person was friendly, like 100%. I've spent 15+ hours on the property, and found very little. The oldest thing I've found was a 1890 Indian head penny, and considering how old the property is and how much metal is everywhere..idk. Is it possible the older stuff is just really deep? maybe the tracker IV just can't pick up on it? I still have to do the field and the front yard, but I think i'm gonna call it quits soon.