cover (one's) tracks (up)
1. Literally, to conceal one's footprints, typically to avoid being followed. Those hounds can track us across rivers, so covering our tracks won't do any good.
2. To conceal the evidence of one's (usually nefarious) actions. We need to cover our tracks before someone traces the bank robbery back to us. I destroyed those incriminating documents to cover my tracks up.
cover one's tracks
Conceal one's whereabouts, activities, intentions, or the evidence of one's involvement. For example, No one knows much about where he's been-he's very good at covering his tracks. This term transfers hiding one's footprints to more general activities. [1870s] Also see cover up, def. 2.