I've always been a bit 'on the fence' about the death sentence; but mostly on the side of 'anti'.
There is no question, in my mind, that certain people deserve to sacrifice their own lives in exchange for their unbelievably despicable behaviour (a current case in Oklahoma City in the US is a good example), but there are many more borderline cases.
I like the look of these cages above, and can imagine them being made a little bigger to contain a sleeping surface, TV (for exercise programmes, and endless replays of The little House on the Prairie), and a secure opening for the occasional slice of dry bread and half-glass of brackish water.
They could be hosed down once a week, be easily moved around by fork-lift truck, and the prisoner need never leave his/her cosy confines. A tarpaulin could also be provided in case of exceptionally harsh weather (if the cages were to be stacked outside).
An economic answer to a very expensive logistical problem... Just an idea!