Hang them
It is the only toned their scourge on free society...
We have to find some solution. In prison, they continue to function within the gang, gaining rank, connecting with other members and "chapters", and eventually getting out, more dangerous than when they entered. Many are US citizens, giving them protection under current law. Maybe imprison all gang members in a fashion that limits any contact with other prisoners. No yard time, meals in cell, no social contact.
No, they should be dismembered in public in the same fashion the do to innocent little girls. These people are butchers and need to be filleted with a dull knife.