I love the idea of a fictional world where sexual slavery is permitted and condoned (ie, you could see someone walking their sub on a leash down Main St. and it would seem normal); however I want to have rules in place to prevent abuse, as I do not find a scene sexy when one person does not care about another's well being to at least *some* degree.

Unfortunately these two ideas are not very compatible (that's why we don't condone slavery in real life, duh :P)

I don't want to get bogged down in too much exposition; I'd prefer to keep the rules of the game simple. What I've thought of so far:

-"Volunteers Only" Only people who want to be slaves are. (Problem: limits story and character possibilities)

-"Professionals Only" Owners are specifically trained and supervised to train slaves. (Problem: same as above)

-"The Check-up" Submissives have to be checked on by a third party regularly. (Problem: they may lie, and it's their word vs. the owner's)

-"No Pain, no Gain" If the submissive doesn't want to do something, they won't get a reward they really want, so the owner knows when they honestly can't take anymore. (Problem: it's not "true" submission)

-"A Worse Alternative" The slave wants to avoid something worse than slavery, so there's an incentive to please the owner. (Problem: the worse the alternative, the worse the worse the potential for abuse)

-"No Blood, no Foul" There are hard limits on what can be done to a slave that are not subjective--no bleeding, broken bones, etc. Anything else goes.
(Problem: you can torture someone without leaving marks)

"Deus Ex BDSM" There's a way to know, to the satisfaction of everyone, when too much is too much and to monitor behavior. (Problem: only works in sci fi or magical settings)

I'm not trying to create a utopia; in fact, the dilemma of abuse could always be an interesting plot point. In the end I guess you just have to pick your poison but what other ideas are out there? Ideas are greatly welcomed.