From WordNet (r) 3.0 (2006) [wn]:
fly the coop
v 1: flee; take to one's heels; cut and run; "If you see this
man, run!"; "The burglars escaped before the police showed
up" [syn: scat, run, scarper, turn tail, lam,
run away, hightail it, bunk, head for the hills,
take to the woods, escape, fly the coop, {break
away}]