Say I have a cologne bottle of 100 ml that I want to carry in my hand luggage on a plane trip.

100 ml is the limit so it should be fine for the transport regulations (if not, please let me know!).

The problem I always encounter is regarding the storage of the bottle: how to prevent it from leaking?

What I normally do is to put it in a plastic bag, so that the possible loss remains there. It is fine, only that the bottle ends up quite wet.

What would be a better approach?