You should consult a local real estate attorney. There is a document you can file on the land records in which you basically state your claim that the fence is on your property which also protect you from the neighbor gaining title to the strip through adverse possession. It is important to know how long it has been there (adverse possession period in CT is generally fifteen years) and how you know that it is on your property (survey?) and what if anything you have done about it in the past. I foiund this summary of the law online, which may be helpfu, it is a little old but should still be accurate. http://www.cga.ct.gov/2006/rpt/2006-R-0032.htm - however as I said you really need to have a real estate lawyer advise you directly on how to handle this. Also you should be aware that it will obviously not make for good neighborly relations if you make an issue out of this, but it is also a good time when the property is being sold to resolve it. NOTE: This information is posted as general legal education, not legal advice.