I'm looking for a word,phrase, idiom to describe a person who doesn't want to share their knowledge to other colleagues and doesn't want to teach others the way of doing something because he is afraid of losing his position in the company or being left behind by his colleagues.
I think of this word: "protective over something". For example in this sentence: My manager is quite protective over his work; he doesn't want to teach me anything.
However, I'm not sure whether the word "protective over" is correct or not. Could you help me out?
Thank you so much.