What's the best way to prevent keyless entry car theft?

How can I protect my keyless entry car from being stolen?

Does keyless entry theft only apply to cars with a push start button?

Does keyless entry theft only apply to cars with a push start button, or all cars that are opened with a key fob? I would like to be clear so that we can take appropriate security action.

Are all cars vulnerable to 'relay' theft?

I've read more and more about the 'relay' method for car theft. Are all cars potentially a target, or only those which have keyless entry?

Jaguar XF (2008 - 2015)

Unique interior. Amazingly quiet and refined. Economy of 2.2 diesel from 2011.