How can I force a slug to update on save
You could write a simple plugin that listened to the onSaveEntry and perform whatever custom business logic you require for slugs.

Don't re-save that entry going through craft()-&gt;entries-&gt;saveEntry(), though, or else you'll create an infinite loop by firing the onSaveEntry event again.

You could either call craft()-&gt;elements-&gt;saveElement() directly or use use QueryBuilder to directly update the database with the slug.