cover (your) tracks

to hide or destroy anything that shows where you have been or what you have been doing.

Roberts covered his tracks by throwing the knife in the river and burying his wife's body miles from his home.

• fire in your
• fire off
• fire off something
• firing on all cylinders
• firm hand on the tiller
• first among equals
• first and foremost
• First come, first served.
• first-come, first-served
• first dibs on
• first dibs on something
• first-hand
• first hand
• [first/highest/next etc.] rung on the ladder
• First in, best dressed.
• first-past-the-post
• first rung on the ladder
• first string
• first-string
• first thing
• first thing in the morning
• first things first
• First things first.
• fish for compliments
• fishing expedition