Just make sure you keep membership card away from other half...awkward to explain...I know from experience !!!
I was thinking same. Have just about kept the punting phone and SIM hidden, but where would you store one of these membership cards???
Inside Tool Box in the Car?
Alternative is simply to take ID with you each time, eg Driving Licence. That way, even if they gave you a membership card, you would simply destroy it, once you return form the party.
With the advent of the smartphones, would it be possible to take a picture of the ID Card, and store it somwhere safe on your phone, then show them the photo on the smartphone when you turn up???
Suppose, where there's a will, there's eventually got to be away??