Are there any other units supposed to be behind that gate?
If not, you can add a pathing blocker using a custom pathing map to fill a large area behind the gate.
This will make all blinks, teleports, whatever search for the nearest valid place to blink to which will be on their side of the gate.
However this does mean that noone is able to be at the other side until the gate is destroyed (when you remove that pathing blocker).
I use this method in a map of mine and it works great, but the gates in my map are simply said, the edge of the map as long as they are alive.