I agree. In our case, we would have said we gave them permission to have their path and playhouse on our land. I think we might have had to charge a dollar in rent too. We didn't end up buying that land so I stopped researching it.
Not necessarily entirely so. At least in some states, how the land is used and allowed to be used may also matter. Where both sides acknowledge the property line is by uncontested use of the land can be more important than what the legal description is.
Here, a simple letter, once a year, to...