Right, so if we're thinking about this like Shikamaru, what steps do we take to stop Rock from (eventually) resolving this internal crisis, thinking "Hey, that was pretty bad for us. I wonder if we can cause it to happen to other people?", and then immediately start working on our tax system in a similar way?
One first-order method I can think of is have the tax collectors keep a year-to-year record of how much they collected from each person and how much they kept vs. how much they gave to the Kage, submitting these records in duplicate along with the tax money. With these records, we can verify transactions easily and have basically the knowledge we need to replace tax collectors if they go missing.
I'll note that an excellent reason to bring up this scheme to Asuma and co. (along with the hydroengineering scheme) is so that we can build defenses so that others can't do the schemes to us.
We should get a census on the population of fire country. That should give us a rough estimate of what we could expect to collect each year.