Oxford Law :: OSCOLA FAQs:
"Be careful when citing URLs. Studies indicate that 'link rot' or 'reference rot' (which is when the url still works but the content is gone) is a major problem.
In Harvard Public Law Working Paper no 13-42, Jonathan Zittrain, Kendra Alberg and Lawrence Lessig report that more than 70% of links in three Harvard law journals do not produce the information cited. As a solution, they promote Perma.cc, which 'will retrieve and save the contents of a webpage, and return a permanent link'. The Perma.cc system distributes 'Perma caches, architecture, and governance structure to libraries across the world. Thus, so long as any library or successor within the system survives, the links within a Perma architecture will remain'.
The original link can be cited along with the Perma link (which is useful as the reader can immediately see the source without having to follow the link to the Perma site), or the Perma link only can be cited (which has the advantage of being short).
This system is preferable to other short url systems that do not indicate the original website and url, and whose future is less certain. The Digital Object Identifier (doi) system used by some journals is also sound, but not all law journals use the doi system, and many of those that do also publish in hard copy and so do not require an electronic reference in OSCOLA.
In general, only include the web address when the document is only available online, when the web address is particularly helpful for finding the document, and when the web address is static (ie not the result of a search in a database). Avoid citing references that end in .pdf. " 'via Blog this'