What Jon Danniken is saying MIGHT be true, depending on where you live.
Both Canada and the USA inherited our system of laws from Britain, and
600 years ago in Britain, forgery was the quickest, easiest way to get rich. With no public education administered by the government and paid for by taxes, few people could read or write. And, that was convenient if you wanted to get rich quick by challengine a will. When rich old Lord Pompous dies, and his will leaves his estate of Blackacres to his son, you show up with a forged will claiming that Lord Pompous had a fling with your mother, and you are Lord Pompous' illegitimate child. And to prove, you show a will signed by Lord Pompous with his customary "X" granting half of Blackacres to you, and the other half to his know son.
Since few people could read or write at the time, it was customary for the wealthy to employ the services of a "notary public" who could read and write and would transcribe a person's intentions to paper and vouch for the credibility of that paper. The problem is that notary publics could be bribed, and so you could often have a half a dozen different wills popping up, each as legitimate on their surface as the others.
The doctrine of Adverse Possession arose as a means of dealing with the problem of widespread forgery. It allowed judges to recognize the claims of people well known in the community for generations to succeed against the apparantly superior claims of total strangers who showed up after a death claiming to be illegitimate children of the deceased.
In Britain and France, up until about 1850, the rights to property were recorded in something called a "land registry" where every time a property was sold or divided amongst heirs or whatever, the bill of sale or will would be registered. So, if you wanted to buy a piece of land, you had to search through all of the bills of sales and wills registered in that land registry for, in some cases, centuries, to prove that the seller of the land really owns what they're wanting to sell. Since that time, however, there have been laws that require that the seller only prove his claim of ownership over the past 40 years.
The problem with that system is that the bills of sale and wills would be damaged by continuous handling, and at a time before photocopiers, often only the owner and the land registry would have originals of the bill of sale or will by which the owner could defend his claim to his land. And, in a fire like the London fire of 1666, which 2/3 of the city went up in flames, then not only did the land registry go up in flames, your copy did too. So, not only did you lose your house because insurance didn't exist back then, you also lost the ability to prove you owned the land you used to live on.
So, in the mid-1850's an Australian by the name of Torres applied the same system that Australia used to register the ownership of ships to land sales and the inheritances of estates. In Torres' system, any time a buyer and a seller agree on the sale of a piece of land, the buyer applies to the "Land Titles Office" to register the sale. The Land Titles Office, which is part of the government, reviews the ownership history of the land to ensure the seller owns it and that there are no leans or other encumbrances on that land. If there aren't any, the land titles office then charges the buyer a fee to register his title to the land. And, with the adoption of that system throughout most of Canada and the USA, most jurisdictions have passed legislation that provides that the title of the registered owner CANNOT be extinguished by adverse possession.
This is a much better system because if the owner of a parcel of land is ever sued, a judge can give the successful plaintiff the right to register a lien against that land at the land titles office. So, if the owner every tries to sell it, the lien holder is payed first out of the sale of the land. Similarily, if a landowner ever goes bankrupt, then his creditors can force the sale at auction of any land he owns to recover their losses. And, since the civil servants working in the land titles office would have no idea if a squatter had been living on that land for the past 25 years, the title registered at the land titles office effectively prevents that squatter from claiming that he now owns the land cuz of adverse possession.
So, if you build your fence where the old fence was, you do so at your own risk. That's cuz if your state or province uses the Land Titles system as opposed to the older Land Registry system, Adverse Possession doesn't apply, and if and when the mistake is discovered, your new neighbors can have you tear down the part of your fence that's on their land.
So, if you live in the older populated parts of US or Canada, like Boston, Philadelphia, New York, Quebec City or Halifax, there's a good chance your city or province still uses the old land registry system. But, if it's the newer land titles system, your title to the land is guaranteed by the city, state or province, and cannot be extinguished by Adverse Possession.
PS: I'm no lawyer, but I read a text called: The Law and Business Administration in Canada Third Edition By J. E. Smythe and D. A. Soberman Published by Prentice Hall of Canada every bit of 25 years ago when I first bought my apartment block, and I still have that book and re-read the part on Adverse Possession and how recording ownership of land has changed over the centuries.