This is about teaching materials — those materials that you've handed out, played, or displayed to students as parts of lectures or tutorials. (These are different to lecture notes, which are written for an academic's own use.)
I'm contacted by academics (particularly those moving to new institutions) about whether they're obliged to provide their teaching materials to their successors? The answer is, probably, yes. That, however, is not the answer to the situation.
Firstly, a little generosity goes a long way. There's no harm in ensuring that a successor has access to your teaching materials.
Generosity, however, does not require anonymity. If your pedagogical efforts are good enough to live on in a unit, then you should be recognised as the creator.
I suggest that you prominently mark all of your teaching materials. For example:
© 2008 Bill Danby (b.danby@universityworkplace.com)
This right of attribution is a "moral right," recognised by the copyright legislation in Australia, the US, the UK, New Zealand, and others. Displaying the year also provides a useful "use by" guide; and, adding an email address ensures that you can be contacted. (If you expect your materials to be used in the UK or New Zealand, you should add, "The author asserts her (or his) moral rights." ▪
A genuine leader is not a searcher for consensus
but a molder of consensus.
—Martin Luther King Jr. (1929-1968)