crazy like a fox
Very clever, cunning, or shrewd while appearing foolish or mad. People thought I was crazy when I told them my idea for massive social networking site—crazy like a fox, more like it! Our boss is crazy like a fox; her daredevil schemes always sound like they'll bankrupt us, but they invariably bring in a huge profit.
Don't let the fox guard the henhouse.
Don't assign the duty of protecting or controlling valuable information or resources to someone who is likely to exploit that opportunity. You're going to put your ex-convict brother-in-law in charge of your business? I can't tell you how to run your company, but don't let the fox guard the henhouse.
fox guarding the henhouse
A person likely to exploit the information or resources that he or she has been charged to protect or control. 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 guarding the henhouse.
fox in the henhouse
Someone with bad intentions. (A fox would prey upon hens in a henhouse.) I'd watch out for him if I were you—he walks around here like a fox in the henhouse.
fox's sleep
A state of apparent sleep (or feigned indifference) in which someone is actually aware of everything going on around him or her. Alludes to the idea that foxes sleep with one eye open and thus are always at the ready. I think Amy is just in a fox's sleep, so be careful what you say right now. The best way to get gossip on these trips is to be in a fox's sleep.