Just adding in there that using PP of moves is an easy and pretty good way to count EVs. Say my Hydreigon has 15 Dark Pulse, and the Pokerus. I fight wild Pokemon, but only Solosis on Route 9, b/c he's being trained in SpA (I EV train for one stat at a time). Note that all of the hits are OHKOs. When Hydreigon runs out of PP for that move, I jot down on my paper that he got 60 SpA EVs. Then I go to a Pokemon Center, heal, and rinse and repeat.
In case anything goes wrong, though, always have at least a sticky not and a pen/pencil on hand.