stay on top of someone or something
1. Lit. to remain positioned on the top of someone or something. Please stay on top of the hill until we call you. The wind is blowing and this sheet of plastic will not stay on top of me, so I am getting soaked!
2. Fig. to keep well-informed about someone or something; to keep watch over someone or something. You have to stay on top of her if you want her to do it right. I will stay on top of this project.