Legal Question in Real Estate Law in Pennsylvania

They would have to do some or all things of the following for 21 years. Further, to acquire that peace of property they need to occupy it and the occupancy would have to be hostile. That is against your interests. Further they would have to be doing so without your permission.

So you could always write them a letter thanking them for mowing your lawn and giving them permission to continue doing so. Once they have permission they can't get the land by adverse possession.

{John}