Playing devils advocate for the argument about big turn (and because I'm still learning planning), how might you plan to set up a batsman to get his wicket?
I remember Warne bowling Strauss behind his legs as he attempts to pad the ball away but it doesn't seem like a strategy you could repeat every time. I know Warne does try it regularly (bowling Gooch in a similar way but with less turn) but surely you would need to set a batter up first beforehand?
Its easier to see a plan using a ball that is intended to only just beat the bat (looking for an edge) or one using variations in speed/flight (looking for the catch from the false shot) but aside from putting a bit of doubt in the batters mind to try and get him to rush out to the pitch of the ball, I'm not sure how I might get a wicket with a square turner?
You're spot on. The answer is, you can't really. A canny batsman will just be sure to position his pads so as to cut off the line of the stumps, and then use the angle you have given him to get the ball away into the gaps.
I coach batsmen on how to play spin, and one of the first lessons is how to use big turn against the bowler.
First thing we teach young spinners is the concept of the dual threat - that is, the importance of attacking both edges of the bat at once. If you're turning the ball two foot, you simply can't do that. One ball is wide outside off, the other is harmlessly down the legside.