A defensive variant rather than an offensive one, this time.
Entrenchment requires three or more pawns in a row – which can include the starting positions. This only applies across a file, and only on the defensive side of the row.
So long as there are at least three pawns, none of the squares they occupy can be jumped over by a knight. Moreover, the pawns themselves cannot be taken by any piece other than a knight. (A softer variant of this allows for the pawns at each end of the entrenchment to still be vulernable.)
Pawns can take other pieces as normal, but to do so may break the entrenchment, making all the pawns revert to their normal status.