The fact that the links of a prong collar can come apart is well known, and most people that advocate the prong also tell everyone that you need a link to a flat collar as a backup. The link actually breaking is another thing entirely of course!
I have had the prong come apart three times in about 2 years of use - the first without a backup (don't ask!) and the last two with the flat collar in use. All three happened on a sigificant correction.
