dragon's teeth

pl n

informal conical or wedge-shaped concrete antitank obstacles protruding from the ground in rows: used in World War II
sow dragon's teeth to take some action that is intended to prevent strife or trouble but that actually brings it about

Word Origin for dragon's teeth

sense 2 from the story of Cadmus
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