This, any physical deterrent, as they will then move onto easier targets.

So there are two types of issues with keyless entry. The first is relaying, whereby a repeater is used to amplify and relay the signal to the vehicle, you can mitigate against this by wrapping keys in tin foil.

The second lies in a vulnerability which can be exploited via the OBD port (which is why some disable them by removing fuse etc) basically it allows someone to start the car without the key being present.

So far as I am aware, some manufactures have released a software update to mitigate this exploit. I do recall that Ford were in denial over the issue, although this may have now changed.

Martin