Keep a lid on it.
Thats between me and the gatepost.
keep that under your belt.
Walls have ears.
It's on a need to know basis, and you don't need to know.!
Keep that to yourself.
Mum's the word.
keep your nose out of it.
Mind your bees knees.
Name, Number,Rank.
loose lips sink ships.

Drink Up Ye Cider.