The only 50-year rule in the Civil Code
The provision below is taken from the Civil Code of the Philippines. The Civil Code of the Philippines is the product of the codification of private law in the Philippines. It is the general law that governs family and property relations in the Philippines. It was enacted in 1950, and remains in force to date with some significant amendments.
Article 605. Usufruct cannot be constituted in favor of a town, corporation, or association for more than fifty years. If it has been constituted, and before the expiration of such period the town is abandoned, or the corporation or association is dissolved, the usufruct shall be extinguished by reason thereof. (Civil Code of the Philippines)
The above 50-year rule relates to usufruct. In property law, usufruct gives a right to enjoy the property of another with the obligation of preserving its form and substance, unless the title constituting it or the law otherwise provides.
Usufruct is a limited real right (or in rem right) found in civil-law and mixed jurisdictions that unites the two property interests of usus and fructus. Usus (use) is the right to use or enjoy a thing possessed, directly and without altering it. Fructus (fruit, in a figurative sense) is the right to derive profit from a thing possessed: for instance, by selling crops, leasing immovables or annexed movables, taxing for entry, and so on.