Password-protect (i.e. encrypt) the documents and provide the passwords on a separate piece of paper with your reasoning and concerns clearly laid out. This won

Password-protect (i.e. encrypt) the documents and provide the passwords on a separate piece of paper with your reasoning and concerns clearly laid out. This won't prevent the leaking of those documents, but it will prevent automatic indexing by search engines unless they deliberately strip out encryption prior to leaking them. If they do strip it out, then the excuses of them "accidentally" leaking the documents becomes very implausible to any reasonable judge. For good measure, add unique watermarks to all documents to make it easier to prove who leaked the documents later.