Yeah, Sexton uses Dave Alred as well. He's a regular biomechanical Yoda -- works with golfers too.
Can you indulge me in a (relevant) family story?
A few weeks back in the QLD rugby club pre-season, I was fortunate enough to get my 15 year old rugby playing son into a Dave Alred-conducted specialist kicking clinic right here in Brisbane. About 15 other boys of varying ages also joined.
My son has some natural kicking ability, though bless him he's far from a young Morne Steyn as yet
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After this clinic - which was as expected demanding and quite technical - he was hugely impressed by what he'd learnt and how he'd been instructed and described Alred as 'Dad, he's a genius coach'. After this clinic, his interest and motivation towards his kicking went way up.
Anyway, some weeks later, playing 10 for his U15 team, he started to be given most of the kicking duties. In his second match, he kicked two conversions from near on the sideline, and the resulting 4 points won his team the really tight match they played wherein the number of tries scored was equal. All parties rather pleased. He would never, ever have achieved this without that kicking clinic.