A Suggestion: Slave collars that influence the wearer.
Some rough examples to illustrate the idea.
Steel Collar: An uncomfortable, tight metal band that inspires fear. With every constricted breath this collar reminds the slave to obey.
Decreases Happiness, Willpower, Defiance, and increases Fear. Due to slightly constricted breathing, the slave can not train Strength or Stamina.
Golden Collar: An expensive and beautiful collar intended to showcase the best slave. Because this valuable collar could easily be sold by an escaping slave for some quick cash, having a slave who wears such decoration illustrates the prowess of her master.
Increases Beauty, Charisma, and Affection. Generates Influence if the slave goes outside the home. Multiplies Escape Chance by 5. (Five times zero is still zero, so if she does not want to escape this is not risky).
Fitness Collar: A technological marvel that tracks a slave's biometrics and provides suggestions for improved performance. The Mastersphere AI can help a slave improve her chances of success when training. Although comfortable to wear, it is not attractive, and the AI can be annoying when trying to perform intellectual tasks.
Decreases Beauty and Charisma. Increased chance of improving Physical Attributes from training. Decreased chance of improving Science/Domestic/Academics from training.
Thought of this when I was playing Free Cities (pgmod) which implements clothing that influences the slave.
Cheers!