If we go a specific skills coach IE Tackling, then it would be wise to look at coaches from other sports like Rugby League. That game is built on tackling and you can see the blokes who grew up with it (eg. Charlie Cameron and Kieran Jack) and their ability to nail tackles. Melbourne Storm are a good example- they hired AFL coaches to teach them to kick and dominated with it (Billy Slater and Cooper Cronk were masters of putting a ball on a dime). They then hired JuJitsu coaches to teach them how to grapple and until many of their tactics were outlawed (crusher tackles, chicken wings etc) but they still had a couple of very successful seasons using those skills.
AFL clubs have been using rugby tackling coaches for decades. Tackling is about intent, you either want to tackle or you are adverse to it. Some players just are not into it and unfortunately we have some of them in our best 22.