Dictionary.com
Thesaurus.com

dragon's teeth

British  

plural noun

  1. informal conical or wedge-shaped concrete antitank obstacles protruding from the ground in rows: used in World War II

  2. to take some action that is intended to prevent strife or trouble but that actually brings it about

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of dragon's teeth

sense 2 from the story of Cadmus

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Both are protected by miles of deep anti-tank ditches filled with razor wire and concrete anti-tank obstacles known as "dragon's teeth".

From BBC

Sharp pieces of slate jut out threateningly against the wall of the house, which Ross described as being "like dragon's teeth".

From BBC

Long ditches lined with coils of razor wire and concrete pyramids known as dragon’s teeth await Russia’s increasingly rare armored attacks.

From The Wall Street Journal

They run alongside raised banks of red earth, deep trenches and neat lines of anti-tank dragon's teeth concrete pyramids.

From BBC

In Ukraine's fourth summer of full-scale war the fields around Sumy are dotted with corn and sunflowers, not yet in bloom, and a crop of dragon's teeth - triangles of concrete which can stop tanks in their tracks.

From BBC