Or to start with a gravity that exceeds the yeasts tolerance, though there's less control this way. - but it's the method I prefer.
Ninjas. But sleeping ninjas, who can wake up without warning.
Best bet is, kill them in their sleep (KMeta) and cut their gonads off (sorbate)
How to tell when they're sleeping? They all lie down together (yeast cake in the bottom of carboy)