One-time taxes are dumb. The organizers of this tax should have the confidence of their arguments to make them permanent, or they shouldn't do it at all.
I guess that by the time a tax had been applied once, the targets would have worked out a way to avoid it anyway.
Apparently, in old Athens, not only were taxes one off, but they were explicitly targeted too, like "It's about time the Alcmaeonids pay for a festival again."
