Best way to measure the unknown length of a coaxial cable?

In a novel about the near future, I speculate that what the media called 'Cyberwar I' has happened and the US government has rushed to throw up a firewall around critical data (military, infrastructure, financial and the like).  This supersecure database would have to have physical connections.  I am postulating that such connections would be through a coaxial cable and that one security measure would be to register all incoming physical connections.  If a bad guy were to splice in some extra coax to access the system, would that addition of coax length be something the system could monitor.  Capacitance? Inductance? Conductance?  What is best?  Would that measure be a function of frequency of the signal (my hazy recollection from having been a ham in my youth)?

 

Thanks

I think you probably need to look to fibre optic cable rather than coax.
In either case Time Domain Reflectometery would probably be used, you need to know something of the cables properties to find distance.
Incidentally, it is probably easier to hack into a fibre optic cable than into coax,
cheers,
Richard