An airtight excuse.
An airtight alibi.
An airtight defense.
We have an airtight argument they won’t be able to punch holes in.
In one system the main cables terminate in large airtight iron boxes placed in the manholes.
No matter what kind of leaves you end up making, be sure to store them in airtight containers (and possibly refrigerate, depending upon ingredients) for safekeeping before the wedding.
You can store the remainder in a Tupperware container, old cream cheese or butter container, or anything else laying around your house that is airtight and able to hold the final product.