Something like a short-range force field. In one episode (I think it was the Mare-do-well episode), you see ponies, mares and stallions alike, working at a construction site, and not all they do can be done by grabbing tools in their mouth. So, magnet hooves.
"Those heroes of antiquity ne'er saw a cannon ball, or knew the force of powder to slay their foes withal. But our brave boys do know it, and banish all their fears, sing tow, row, row, row, row, row, for the British Grenadiers."
And when the siege is over, we to the town repair. The townsmen cry, "Hurrah, boys, here comes a Grenadier ! Here come the Grenadiers, my boys, who know no doubts or fears ! Then sing tow, row, row, row, row, row, the British Grenadiers.