Sounds like you've done the "give him rope, and let him hang himself" thing to a degree... maybe some furthering of this then (if no success) following Fokjok's suggestion.
For example: where I fly (YSBK) there's another field (YHOX) that, with a strong south-easterly, becomes EXTREMLY turbulent on short finals (i.e. +/- 150' with a relatively experienced instructor flying). That wind is easy to handle on departure YSBK but can scare the crap out of you at YHOX... AND the ground is very close... just be ready to take over in case he decides to keep going!