Adverse possession laws vary by state. In Michigan the homeowner has to prove that he gave permission, unless the possessor acknowledges that he did. A dated statement signed by the possessor is best. Proof of delivery of a registered letter sometimes works. The time of possession must be at least 15 years, so the permission has to be renewed within that time, and the clock would start over.
Worked on a title claim once where a 3x wide gravel drive was between house A and B. House A had used the entire driveway for 20 years for parking. House B had its own driveway on the other side of the dwelling.
House B sells to new owner and finds out 1/2 of house A drive belongs to house B. Title claim is made and it goes to court. The Judge ruled house A was entitled to ownership of the entire driveway right up to the edge of the B dwelling.