User blog comment:Albierio1292/Stopping the Corruption Hallow Spread/@comment-4671744-20111211214034/@comment-4562735-20111211222551

Pake a 1x4 hole in the ground, then place a block that doesn't spread corruption in said hole. Also make sure that there is NO grass under those blocks (Corrupted/hallowed/normal) because it will eventually spread too :)