Mudguard, assuming that you know the word "kayak" as the small one or maybe two person skin boat made and used by Eskimoes, we'll go on to the pun involved.

It's a punning change on "You can't have your cake and eat it too," an extremely common folk saying in English, which means that you can't dispose of a good both by consumption and preservation; you've got to choose.

Dave Oesterreich