What does 日食大水則鼓於用牲於社 mean?

In "Du's Handbook of Classical Chinese Grammar," the following Chinese sentence and English translation appear, minus the Korean pronunciation:

日(일)食(식)大(대)水(수)則(칙)鼓(고)於(어)用(용)牲(생)於(어)社(사)

“For eclipses and floods, we beat the drums and furthermore make sacrifices of livestock to the land god.”

The above sentence was supposedly an example of 於 (어) being used as a conjunction between two clauses with the meaning of either "and" or "moreover," which implies that "Du's Handbook" believed 用 (용) was being used here as a verb. I disagree, and would like to suggest the following translation:

日(일)食(식)大(대)水(수)則(칙)鼓(고)於(어)用(용)牲(생)於(어)社(사)

“The rule for eclipses and floods (日食大水則) [is] to beat drums (鼓) at (於) a sacrifice of animals (用牲) to (於) the land god (社).”

日食 (일식) means "eclipse," 大水 (대수) means "flood," and 則 (칙) means 법칙 (法則), which translates as "rule" or "law."  用牲 (용생) means "to sacrifice animals," but because of 於 (어), which means "at," we can assume 用牲 (용생) was being used here as the noun phrase "a sacrifice of animals," not as the verb "to sacrifice animals." In other words, there was no need to create a new usage for "於 (어)."