A fence is not required it seems in PA but GM needs to be able to show exclusive use---
"It is well settled that a party claiming title to real property by adverse possession must affirmatively prove that he or she had actual, continuous, distinct, and hostile possession of the land for twenty-one years. Fred E. Young, Inc., v. Brush Mtn. Sportmen's Ass'n, 697 A.2d 984 (Pa.Super.1997). Each of these elements must exist, otherwise the possession will not confer title. Id. An adverse possessor must intend to hold the land for himself, and that intention must be made manifest. Id. Broadly speaking, actual possession of land is dominion over the land; it is not equivalent to occupancy. Id. There is no fixed rule, however, by which the actual possession of real property by an adverse claimant may be determined in all cases. Id. The determination of what constitutes actual possession of property for purposes of adverse possession depends on the facts of each case, and to a large extent, on the character of the premises. Id. The words visible and notorious possession mean that the claim of ownership must be evidenced by conduct sufficient to place a reasonable person on notice that his or her land is being held by the claimant as his own. Id. To constitute distinct and exclusive possession, it need only be a type of possession which would characterize an owner's use. Id. Further, in order for adverse possession to ripen into title, it is necessary to show that such possession has been continuous and uninterrupted for the full statutory period. Id. In this Commonwealth, the statutory period is twenty-one years. The law does not require that the claimant remain continuously on the land and perform acts of ownership from day to day. Id. The word "hostile," as an element of adverse possession does not mean "ill will" or "hostility," but implies an assertion of ownership rights adverse to that of the true owner and all others. Glenn v. Shuey, 407 Pa.Super. 213, 595 A.2d 606 (Pa.Super.1991). If all of the elements of adverse possession other than hostility are established, the element of hostility is implied. Id. However, it is important to note that where a familial or fiduciary relationship exists, permissive use will be presumed, thereby negating the element of hostility. Waltimyer v. Smith, 383 Pa.Super. 291, 556 A.2d 912, 914 (Pa.Super.1989)."