It sounds as if the incursion occurred not because the instructor wasn't looking out as he entered the runway, but because he was distracted and didn't realise he was entering the runway. That's a significantly different issue.
How on earth do we manage at a plain old grass gliding club when the thermals quit and all the gliders come down more or less at the same time without running into each other on the ground????
Or maybe the answer is that you don't?
Here's an LAA document about aircraft collisions:
http://www.lightaircraftassociation....raft%20V10.doc
I quote:
Of the 178 aircraft involved, 72 were powered aircraft, 6 were glider tugs, 96 were gliders, and 4 were military. The military aircraft were 2 Tornados, 1 Tucano and 1 A-10
And relating to gliders specifically:
84 collided with other gliders as follows:
- 16 on launch, landing, departure of approach
- 34 in local thermal
- 10 on a local ridge
- 10 near the launch site
- 14 in cross country thermal