Sheikh Mogra said grooming should be seen purely as criminal behaviour, and using "labels of race or religion" could "drive the problem deeper underground".

BBC: Shaykh Ibrahim Mogra of the Muslim Council of Britain

If he only wants to take the skeleton and try to put an end to the black market, he will have a fight and will only drive the black market deeper underground.

NEWYORKER: Bones of Contention

Mr. BENJAMIN JOHNSON (Immigration Policy Center): When state and local officials begun their own roundup and their own sweeps, it makes it more difficult to deal with undocumented immigration because it drives people deeper and deeper underground.

NPR: U.S. Communities Act on Immigration Issues

Today, his story offers a rare inside look at an extremist movement that flourished in the U.S. And it raises questions about how it managed to spread undetected in the U.S. and whether, since Sept. 11, it has simply moved deeper underground.

CENTERFORSECURITYPOLICY: An insight into the fifth column

Zhao further envisions going even deeper, to enable underground spaces with multiple levels.

CNN: Why Singapore is putting its oil back into the ground

They now have to dig deeper and deeper into the ground to make wells, as the underground water is sucked dry.

NPR: Chronic Water Shortages Hit Rural Chinese Hard

Building underground is no easy task, especially the deeper you go.

FORBES: Underground Living is a Solution in Search of a Problem

Future NASA and ESA missions that are planned for Mars will have to dig deeper to search for evidence of life, which may still be taking refuge underground.

FORBES: The Surface Of Mars Is Too Dry For Life

Grossman has followed this up with a sequel, The Magician King, which delves deeper into both the world of Fillory, the underpinnings of magic, and the magical underground that operates outside the scope of the magician academy.

FORBES: Lev Grossman on 'The Magician King' and the Science of Magic