The Dispersion Ring is a small metal ring, often made from enchanted steel or lead, that will prevent a unicorn from using magic when placed around their horn. These rings are often used on unicorns who have been taken prisoner, whether through the penal system or in times of war or slavery. However the ring has garnered infamy for it's use as a fetish.
The physical band of metal around a unicorn's horn is usually enough to cause a unicorn's horn to short circuit when ever they attempt to cast a spell. However Dispersion Rings have other anti-magic properties as well.
The Steel Dispersion Ring is enchanted with an anti-magic spell, as well as a spell to prevent the wearer from removing the ring.
Some Dispersion Rings are also made from lead. The magic absorbing properties of lead prevents the ring from being enchanted to prevent the wearer from simply removing the ring, and as such Lead Dispersion Rings are far less common and mostly used by non-magical races dealing with unicorns.