Meaning: conceal one's whereabouts, activities and intentions.

Example:
The murderer covered his tracks by throwing the shot gun in the lake and burying his landlord's body.

Meaning: to reveal the true identity. To put a damper on someone's plan to conceal something.

Example:
1. The custom's officer recognised the man from a wanted poster and blew his cover right out.
2. She did not intend to blow his cover but then her habit of blabbering did not help.

Meaning: make plans based on events that may or may not happen. To start making plans about something that is based on something in the future which may or may not happen

Example:
1. It is not good to start counting your chickens when you do not even have the cash to start your own venture.
2. She has been counting her chickens before they hatched and has already bought a dress even though nobody has asked her to the ball yet.

Meaning: a chronic television viewer. Very lazy person.

Example:
1. My younger sister is a great couch potato; she can watch TV 24 hours a day.
2. It is a matter of debate if couch potatoes are less intelligent than their brethren.