More can always be said on the matter; if anyone can post about serfs and relevant enforcement, please do go ahead! For the meantime, we do have a few previous posts on this matter. Both these posts look more at how a serf might become not a serf, but they by necessity also deal with how they were kept on.

• u/chevalier-sans-peur looks at Medieval France and England;
• and because this is Medieval, u/sunagainstgold of course has something examining this as well.