From Longman Dictionary of Contemporary Englishtake matters into your own handstake matters into your own handsDO something/TAKE ACTIONto deal with a problem yourself because other people have failed to deal with it Local people took matters into their own hands and hired their own security guards. → matter
Examples from the Corpus
take matters into your own hands• The city council took matters into its own hands and set a date for the meeting.• The last thing leaders want is Tutsi who survived the genocide taking matters into their own hands.• As a result, some countries have taken matters into their own hands.• When the psycho is caught, then let go on a technicality, Mom takes matters into her own hands.• So why not take matters into our own hands?• She was more than capable of taking matters into her own hands.• She then took matters into her own hands.• Finally the women of Buntong Tiga can stand it no longer - they take matters into their own hands. 