Which preposition to use with oppugners

of Occurrences 2%

Dennis, the fiercest oppugner of puns in ancient or modern times, professes himself highly tickled with the "a stick" chiming to "ecclesiastic."

on Occurrences 1%

Revenge and malice were as two violent oppugners on the one side; but honesty, religion, fear of God, withheld him on the other.

Which preposition to use with  oppugners