Ev training is a big part of PRO gameplay.
With this being said iam really happy/satisfied that there are a lot of "Ev traing hotspots", the only problem is traing Def, since there is no place where only pokemon who held this Ev spawn, besides that, one of the most commun pokemon used to train it is Geodude"gifted" with the ability "sturdy", wich makes trainig even harder. There is also the fact that tank pokemon are the ones who benefit more from Def and also the hardest to train.
So my sugestion is that in addition to the macho brace you implement the "power belt" (Reduces Speed by 50%. Grants 4 Defense EVs when the foe is defeated). There are similar items but for the other Ev although i dont think there is any need for them.