Mage-raised vertical dirt wall thrown up in seconds to stop the rolling behemoths short of the trench.
With the Juiced Rot Sticker Behemoths closing and every arrow, bolt, and spear proving useless, a group of mages far to Carl's left casts a spell that raises a spine of dirt into the air like a physical wall between the trench and the onrushing attackers. It climbs ten feet, crackling loudly as it builds itself, blocking the defenders' view.
The pets hit it a moment later. Some ramp up off it and launch into the air; the rest crash to a stop against the dirt, a few detonating and showering rock and gore. The airborne ones mostly fall back on the enemy side, where thorns as thick as Carl's arm sprout from the earth to engulf them — before The Frothing Tunnel Moles blow the whole line.
A crackling vertical spine of packed earth rising ten feet in seconds, later sprouting arm-thick thorns.
The improvised barrier that halts the pet-bomb charge and sets up the buried-explosive detonation.