keep (someone or something) in sight
1. To position oneself to be able to see someone or something. Keep the thief in sight while I call the police.
2. To remember or remind oneself of something. If you don't keep your goal in sight, you'll give up before you can ever achieve it.
keep someone in sight
to make sure that a person is visible at all times. He looks suspicious. Keep him in sight at all times. I cannot keep him in sight day and night.