1. A method, performed on a computer system, for watermarking content stored in a plurality of corpora each having a plurality of corpuses, the method comprising: using the computer system to perform the following: receiving a data set of content from a corpus within one of the plurality of corpora; applying the data set to a natural language processing (NLP) stack including a plurality of NLP analytics each analyzing the data set; generating a feature watermark from each of the plurality of NLP analytics; and forming a watermark tree from each of the feature watermarks, the watermark tree representing a hierarchical relationship between each of the feature watermarks generated from each of the plurality of NLP analytics, the watermark tree defining hierarchical pointers that point out inherited watermarks that exist between the feature watermarks according to the hierarchical relationship, the watermark tree including a time stamp specifying a time that the data set was accessed from the corpus.