Prochorus implements the abovementioned plan with life-linked sponts. One exception: he ups the Size to +2 for level 15. That should get it done in two castings, right? He tries to choose a time when the wind blows the sound away from the village and tries to make sure there is no one nearby.
Life linked spont: pe 5 + sta 1 + kantele 3 + voice gesture 2 = 11, against total 15.
He rests between the castings, obviously.
I'm assuming he tries to do this in the evening or at night, when there aren't any workers nearby?
It's a spont, so your total should be divided by 2 after the die roll.
Rolls are 7 and 4, for totals of 9 and 7.
He loses 3 Fatigue Levels at each casting.
This saves about 2 months of labor but, from what your grogs report back to you, the workers comment a lot on how this rock became so much easier to remove overnight. Lothar tries to explain it as a special technique or some such, but his explanations are less than convincing...