What do you meant by "prevent" ?
Unit gets pushed when nearing the region ?
Unit dies when enters the region ?
If you follow Maker's trigger, the unit will be moved instantly to the direction behind the unit by X offset.
But if you use this trigger, it's dangerous because if your unit is knockbacked by another trigger, entering the region with the angle of the unit facing behind, the trigger will move the unit closer to the "forbidden area".
But this will unlikely to happen.