pukki kaalimaan vartijana

Literally, “a billy goat guarding a cabbage patch.” Compare Hungarian kecskére bízza a káposztát (literally “to entrust a goat with the cabbage”), German den Bock zum Gärtner machen (literally “to make the goat into a gardener”).

pukki kaalimaan vartijana

1. (idiomatic) fox in the henhouse, fox guarding the henhouse (someone untrustworthy placed in a position of trust in which they will be harmful, damaging or detrimental to benefit themselves)

The verb of placing someone as the "billy goat to guard a cabbage patch" uses the translative case for vartija instead of the essive case:

panna pukki kaalimaan vartijaksi ― to set a fox in charge of guarding the henhouse

See pukki.