You need to move the hive further away (miles) if possible. If this is not possible, move more bees to the new location when you make the splits to account for some moving back to the original hive. Also remember that only field bees will return, so try to move more of the nurse bees (uncapped brood) to the split in the new location.
You could also try moving both splits so that there is no original location for them to return to, but this might mean more drifting into other hives. Also put some brush/weeds in front of the hive entrance so that they will take new bearings as they leave the hive.