This is actually a problem in scientific note taking and the very simple rule is you write all notes in pen and if you are needing to remove text you only use a single line to cross it out. That way if someone scribbles out the words/data you know it was tampered with as opposed to modified by the original writer. It also helps to put your initials on every edit and sign the end of the page, as well as have a witness sign the end of the page (but that may be excessive in your case). Also use only bound notebooks with numbered pages that are obvious if a page has been removed.