I've never heard of this strategy before, it certainly seems a little far-fetched to me (despite my love of Star Wars & countless hours performing similar feats in Rogue Squadron.)

Perhaps Duncan was referring to the Battle of Asculum, between Pyrrhus and the Romans in 279 BC? There the Romans made special anti-elephant chariots, or war wagons, fitted with long spikes and towers for archers. However, the men on these wagons were picked off by the high-up archers on the elephants, and the Epirote light infantry.

I can discuss some more traditional anti-elephant tactics. It must be remembered that elephants were a particularly volatile arm of warfare, liable to panic, and so they could be easily countered by disciplined troops.

At Zama, for instance, Roman commander Scipio Africanus had his men blow loud trumpets at the approaching elephants to unnerve them and then had his men split up, making gaps through which the elephants could pass. The scared elephants avoided the soldiers and went through the gaps to the rear of the Roman army, where they were dealt with.

Light infantry were also often used against elephants, peppering them with arrows, javelins and sling stones. This constant harassment could kill mahouts and scare the beasts, often driving them into the ranks of their own men.

Perhaps the most bizarre way to stop elephant attacks was used by the people of Megara against Antigonus II in 266 BC. The Megarans, knowing that elephants were frightened by the squeals of pigs, set a herd of swine alight and drove them towards the Macedonian elephants, which drove them off.

Sources: Plutarch's Life of Pyrrhus and Adrian Goldsworthy's The Punic Wars