@Dewain J. fortunately for you Pennsylvania requires 21 years to adversely possess real estate (one of the longer periods in the country),
http://legalbeagle.com/6581465-pennsylvania-squatters-rights.html
though the Pennsylvania Bar Association wants to reduce the time required to adversely possess.
http://www.philadelphiabar.org/page/BoardResolution1138206252004?appNum=5
My own response would be to verify and prove the key fact -the location your property line first (before getting a lawyer). I would also verify in person with your local permitting agency whether a fence building permit was required and what actions the agency is able to take as well as what they are likely to do if a complaint is filed.
If you are certain on where the property line is, take your information as politely but as directly and unequivocally as possible back to your neighbor along with a specific demand, a deadline, and a clear statement of what you intend to do if you and your neighbor can not come to an agreement. For example, tell your neighbor what you understand the situation to be (Our mutual property line is between these two points and your fence is x' on our side of the line), what you are asking the neighbor to do (I'd like you to join me this weekend in moving the fence back to your property. Offer to provide the beer and brats.), when it must be done (This must be resolved by Wednesday), and what you will do if an agreement can not be reached. (I will proceed to file a code violation complaint regarding your fence with Code Enforcement, my Attorney (give him your Attorney's business card) will commence a trespassing civil suit against you seeking $XX,000 in damages and fees), and I will personally call the police and file a criminal trespassing complaint against you with XX law enforcement agency. I prefer to work with you cordially. However, your fence is on my property, here is the proof. Let me help you move it back to your own property line.
It is not known whether it will be necessary for you to defend against a claim of adverse possession. If you must here are some facts to consider as suggested in the legalbeagle.com link above.
Remedies
The original owner of the land has a few options to cure an adverse possession and evict the claimant, but these actions must be taken before the 21-year deadline.
- Proof: The true owner first must prove that some or all of the adverse possession criteria have not been met. For example, the owner might show that the claimant hasn’t possessed the property for the full 21 years or hasn’t possessed it continuously.
- Permission: The property owner might also consider giving the claimant permission to use the property and to get him to document this by signing an agreement. This establishes the claimant's knowledge of the true owner of the property and eliminates the “hostility” of the possession, knocking out two of the necessary qualifications.
- Lawsuit: The third option is to take legal action, such as filing a trespassing lawsuit or an injunction that bans anyone from using the property. This establishes legal ownership of the property and provides a way to start the eviction process. Plaintiffs can also request a jury trial to decide ownership.
Good luck. Let us know how this situation works out for you.