Then you shift gears and blame the teachers unions for protecting bad teachers that ought to be fired and dig into the all-too-deep trough of anecdotal evidence to dredge up a few examples of really bad teachers that were hard to fire.

FORBES: A Response to Megan McArdle

But it was only three years ago that vents were first detected in the Cayman Trough, a deep trench formed by the boundary between two tectonic plates.

BBC: Deepest undersea vents discovered by UK team

While shallow-rooting plants, like succulents, can thrive in a low trough, the roots of dwarf evergreens need a container at least 9 inches deep.

WSJ: Trough Gardening: A Challenger to the Terrarium Craze?