Make a rect in the shape of a wall and make a trigger like this:
Events:
Unit enters 'Rect'
Conditions:
Owner of entering unit = Neutral Hostile (Player Comparison)
Actions:
Move unit instantly to (Point with Offset) Position of entering unit offset by ..., ... (x, y)
If they come from above: 0, 75
If they come from beneath: 0, -75
If they come from the right: 75, 0
If they come from the left: -75, 0