I believe some states have laws to confine these perps, after their criminal sentence, under civil laws.
Like you would confine a mentally-ill person that was "a danger to themselves and others."
Sex-crime recidivism is so high, that civil confinement suits me just fine.
Two strikes and life, AFAIK. Maybe one strike?
How about one strike and your dead. Commit a violent felony, any violent felony, and you are permanently removed from our planet.