Tammy: It’s slaves who belong to foreigners. Every now and then someone decides to escape and there’s a bit of a fuss, since Roald instituted the policy of never returning runaways, and Jon continues to carry it. Instead the Crown quietly purchases the runaway and has the runaway work off his debt. If s/he has children and dies before the debt to the Crown is paid, the debt’s written off–the kids don’t have to pay whatever remains.
Not that many slaves who travel with their masters are interested in escape, unless they know they can make a good living as free people. Slaveowners must care for their aged and infirm slaves, but free lords do it only if they feel like it. Masters won’t treat a valuable slave badly, any more than you’d put a ruby bracelet in the dishwaster: valuable property gets treated as valuable, whether it’s human or otherwise. Of course, no slaveholders will bring field hands, mine workers, ships’ slaves, and others at hard labor to Tortall. They’re far more likely to run.