Be looking over your shoulder
Definition 1 of 2
Pro Tip 1/3Fearful Vigilance
Implies one is anxiously aware of possible threats, often because they've done something wrong. 
Ever since the scandal, the politician has been looking over his shoulder.
Pro Tip 2/3Avoiding Trouble
Reflects the attempt to avoid being caught or facing consequences. 
After hacking into the system, she spent months looking over her shoulder.
Pro Tip 3/3Stressful Caution
Indicates a prolonged state of stress due to fear of being pursued or harmed. 
He's been looking over his shoulder since he witnessed the crime.