Stock units are able to be hidden from Agents and Guest. The hidden Stock Unit will still be visible on your main booking calendar as long as it is Active.
Go to Settings > Stock Configurations > Stock Units.
Once here, select the stock unit that you want to make hidden.
Scroll down the page, and you will see the "Hidden" option on the left-hand side.
Just select "Yes" and the stock unit will become hidden to guests and agents.