Chastity & Denial

Of all my kinks and fetishes, chastity takes a special place. There's really nothing quite like it:

It's a body function that can be denied long-term. At most, a slave can be denied air for a few minutes, bathroom use for a few hours, and food for a few days. Yet, his orgasm can be denied for weeks at a time, maybe even longer.
It's low-overhead. I suppose a slave can be denied hearing, or eyesight, or the right to speak for more than a few days at a time, but unless the slave has prior practice living in silence or darkness, it takes preparation on both the master's and the slave's parts to achieve such a feat. In contrast, chastity can be as simple as telling the slave not to cum.
It's discreet. There's no obvious sign that a slave is in chastity, which means it can become a discipline with minimal disruption to life. In fact, given the popularity of the kink, it's very probable that someone in your social circles is secretly under order to remain chaste. (It brightens a dull day to try to figure out who it is.)

There aren't many kinks that share these traits. Chastity truly is unique.

Terminology

"Chastity" or "denial"? While the two words aren't completely interchangeable, there is a large overlap. Personally, I like the word "denial" better when the context is clear. For one, some people use "chastity" as a shorthand for "chastity cages" or "chastity belts", which is different from the concept of "not having orgasms". For another, "chastity" describes what the slave does, while "denial" describes what the master does. It's the master who is denying the slave the privilege of orgasm. It has more of an emphasis on the power dynamic.

Device or no device?

Chastity without device? Simple: just tell the slave to keep his hands off his dick.

There's no device that's truly inescapable. If nothing else, most padlocks can be easily picked. There's also the matter of hygiene. The slave needs to be regularly unlocked for cleaning, which disrupts the ideal of long-term uninterrupted wear. All arrangements of sexual denial ultimately come down to some level of willpower.

That being said, using a device has a few benefits:

Most devices make it painful to have erections, which is a nice torment.
It is a physical object locked onto the slave's body, which serves to reinforce his submissive mindset.
It does set up a barrier, which makes it less likely for the slave to accidentally pleasure himself, or to cave during a moment of weakness.
On some level, the cage's presence is proof that the slave hasn't cheated. Even if the slave knows how to pick a lock, it still takes non-trivial effort to do so without being discovered.

However, in my mind, device-free orgasm denial is the ultimate demonstration of the master's power over the slave. The slave is bound by the master's words alone. There's no lock to pick, because the lock is in the slave's head. Erections are meaningless without master's approval. Master's whim is slave's reality; no physical lock can achieve that.

Stimulation

If a slave is denied orgasm without a device, a generous master might allow him to freely stimulate himself as long as he doesn't cross the line. Though not a substitute for the ultimate relief, stimulation still feels nice and is usually desirable. It's a privilege the slave should be grateful for.

However, the slave might find it difficult to enjoy this privilege in moderation. If the slave repeatedly cums without permission, the master might revoke this privilege. Alternatively, the slave might find it easier to voluntarily abstain from stimulation altogether. In either case, supervised edging can be used to remind the slave what he's missing.

If the master can't be bothered to edge the slave, he can tell the slave edge himself. Make the slave signal when he's within X seconds or strokes from ejaculating. By default, the slave must then halt stimulation, cool down, and start again, but the master can issue a command to cum. If the slave can't, he's punished. The smaller X is, the more difficult the game is.

The Paradox

Supposedly, the promise of an orgasm is this carrot a master can dangle in front of his sexually denied slave, in order to goad the slave into good behavior. Of course, since the arrangement is fundamentally voluntary, on some level, the slave must want not to cum.

Most often, this is like a smoker trying to give up smoking – having one would feel good in the moment, but not having one will feel good in the future. Sometimes, the slave is proud of how long he's lasted and might not want to give up the streak. In any case, the slave might not mind being denied a bit longer. He might even turn down a chance to have an orgasm.

However, surrendering orgasms means surrendering all of it: both the freedom to cum, and the freedom not to cum. It's not his call anymore, in either direction. If the slave's motivation is unclear or fickle, why not try incorporating an external trigger:

Roll a die and let chance decide. Roll a 6, have an orgasm.
Set a schedule. The slave is given an orgasm (or a dice roll) once a week / a month / a year.
Earned release. The slave is given an orgasm (or a dice roll) after accomplishing a set number of tasks – 500 miles chauffeured, 50 massages given, 5 hours of stress position, etc.

Complete denial is also an option. It's no easy feat for the slave to be denied indefinitely with no relief, and, ironically, this would mean the master is denied a means of control, but it could make for a solid foundation for other aspects of the D/s relationship.