Ignore clients who bring you more worries than money. Hire someone to answer these questions. If the income from such clients does not cover the salary of such a person, ignore such clients. Another approach is to create a template document describing your security practices based on an analysis of such questions, and send it in response to such questionnaires with a cover letter saying that you are very sorry, but answering the questions takes too much of your time and it'll be a pity to lose a client if this PDF is not enough for him. In any case, all that paper exists to cover someone's ass, no one will read your answers.
The need to hide cables under water exists, among other things, because satellites will be the first thing that will fly down in the event of a global conflict. Of course, underwater cables also have their vulnerabilities, but at least the technology for repairing them and laying new ones is much simpler than satellites.