From Longman Dictionary of Contemporary Englishbe looking over your shoulderbe looking over your shoulderto feel worried that something unpleasant is going to happen to you → shoulder
Examples from the Corpus
be looking over your shoulder• So, reading through this book, you feel as thought Alwyn is looking over your shoulder, egging you on.• Two snub-nosed bristle-headed boys were looking over my shoulder in bright-eyed interest.• I am looking over my shoulder.• You were looking over your shoulder waiting for the knock on the door. 