a fox in the chicken coop

Someone who will or intends to exploit or manipulate something, some place, or someone for their own personal gain. (A fox inside a chicken coop would prey upon the chickens.) He was like a fox in the chicken coop, using every trick up his sleeve to line his pockets with the company's money. Giving a person like that access to so much power is like putting a fox in the chicken coop. My sister is going to put her ex-convict brother-in-law in charge of her business, and I'm worried he'll be like a fox in the chicken coop.