be looking over your shoulder
be looking over (one's) shoulder
To be maintaining an anxious vigilance (perhaps to the point of paranoia) to monitor what others are doing or might do. With all these bright college grads coming into the company, you better be looking over your shoulder.
be looking over your shoulder
If someone is looking over their shoulder, they feel anxious all the time because someone might hurt them or cause problems for them. When a company keeps making people redundant, those who are left behind start looking over their shoulder. You'd be on the run for the rest of your lives, looking over your shoulder at every turn.