It depends what you mean by it. If you mean physically, e.g. to avoid bullets or hitting your head on a doorframe: You have to keep your head down You have to duck If you mean metaphorically, e.g. to avoid being noticed by your boss and asked to work overtime: You have to keep your head down You have to stay under the radar There are many ways to say this in all honesty. It depends on the speaker's style

Hey there, if you mean to stay down then this is fine. Ex. You have to stay low so you don't hit your head. Ex 2. You have to stay down/stay low so they don't see you.

Your meaning is unclear. This is not an expression that we would use in English - but I am guessing you may mean "to lie low" - this is a metaphor for acting in a way that does not draw attention to you. For example, the celebrity cancelled their public appearances and decided to lie low after receiving lots of negative publicity.

Honestly, this sounds fine to me. You could also say, "You have to stay down." or "You need to stay down." It depends on what context you're using.

You have to keep a low profile.