on look-out?

[Kristine May]

Is this correct?

Leon’s men stayed where they were hiding, on look-out.

Also should it have a hyphen, as in look-out?

Thanks!

[Uncle M]

No hyphen needed. As a noun, meaning a person who is on watch or the state of being on watch, it's one word - lookout.

As a verb it would be 2 words: Look out for thieves.