Ah, the castrati method. I prefer the Pulp Fiction "pair of pliers and a blowtorch" method for terrorists myself.
I think the traditional English punishment for treason was very effective.
First stretch out the convicted on a table in public view.
Castrate the convict and display the testicles to the convict.
Feed the testicles to stray dogs.
Slice open the abdomen of the convict.
Pull out the intestines of the convict and burn them before the eyes of the convict.
Behead the convict and place the head on a pike for the crows to feast upon.
Quarter the convict and send the four and send the pieces to the four corners of the land as a warning to those who would defy the King.