1. Indefinite Destination
Through Indefinite Destination, a person or group of people are technically en route to their destination, and until they are no longer in transit, they cannot be tried, arraigned, or otherwise shuffled through the justice system. They have no legal rights, and are glorified human cargo. The trick is an excruciatingly slow method of transport that renders the passengers remote from society and detached from access, like a ship. The turn is that the ship doesn't actually have to go anywhere, it can sit out in the water for weeks, or months at a time, and it can be resupplied, and the crew changed over via supply boats, leaving the passengers stranded at sea in something actually worse than a prison.
If questionable news sites can be trusted, the US Coast Guard is already doing this with suspected drug traffickers and smugglers, seizing their ships and cargos, and taking their crews as captives aboard coast guard cutters that stay out for months.
2. Labor Camps
Rather than locking low threat criminals and dissidents in jails, they can be moved to heavily policed settlements where they are put to work doing various things for the people that own and run the camps. This can range from the civic minded ecological clean up and recovery actions, to building houses and settlements to be later occupied by suburban minded Urbanistas, to Gulag style slave labor in actual mines or Southern style agricultural slavery.
The USSR did this one extensively.
3. House Arrest/Social Ostracism
A form of self-detention, the dissident is made the subject of the daily discourse and through social pressure and hostility, they retreat into their homes and silence rather than face the hue and cry of the public. This can range from producing an internet scandal (the female vet who crossbow hunted feral cats) to a public scandal (producer sexual coerces up and coming starlets) to whatever is deemed to work. The individual is discredited, and ripples run through the fabric of society.
Just turn on the TV.
To confine or restrict a group, in this context, a section of the population is isolated economically and socially. This both minimizes their public voice (oh, them, ugh, such animals) and limits their interaction with other people outside of their section. In the US this is predominantly applied to black people living in income limited areas, with substandard access to education and employment, and being highly reliant on welfare. Outside of this context, any social group can be placed into a ghetto where their voices are ignored, and their social values are trod down by the self proclaimed righteous.
Just turn on the TV.
5. The Chinese Option
China has maintained a strong control over it's massive population for centuries using a trio of techniques: disarm, demobilize, de-educate. Disarmed populations cannot rise up and fight back against an oppressive government. Demobilized people cannot relocate themselves to areas of better opportunity, and have to accept whatever living conditions exist where they are. De-educated people enjoy their bread and circuses and do not question their masters. The masses become the inmates of a prison state. Actual prisons exist, but these are far more for political dissidents and rebels within the government than for actual criminals.
Another mass shooting, CAFE standards and electric cars, and Keeping up with the Kardashians
6. To the Colonies
The problem with prisons is that they are resource sinks, and keeping people in bondage prevents them from doing something useful to the state, other than justifying the police and for profit prison system. Where there is colonial expansion, there is a need for people to be in those colonies. Removed from the home state, the dissident and criminal is forced into a situation where their continued survival is beneficial to the colony, and vice versa. The colony is governed by military and colonial forces, and everyone is bent to common goals of survival, and eventual prosperity. Should the colony fail, it is only criminals and agitators who die.
England did this extensively, and used such practices to colonize Australia and North America. Likewise in the Cosmic Era, the colonies of the Atlantic Federation across the solar system are being populated with clones, insurgents, dissidents, and people who aren't willing to get with the big happy picture.
With things like brain implants, behavior controlling chips, and psychotronic programming, even the most rebellious dissident can be made to love Big Brother. The downside to augmentation is that it is expensive to do, and is really only feasible on the small scale. There aren't going to be assembly lines were rows of nurses and robo-surgeons methodically saw people's heads open to make alterations and then put them back together. The reward isn't worth the cost and effort, and the public would not support such a gross violation of humanity. This treatment is used as a deterrent to others, showing that the state is willing to turn someone's brain into salsa and make them a puppet, a show of power. It is also used on people who are too valuable to just turn loose, execute, or lock up in a prison.
Nerve Stapling is the quick and dirty version of this.