Invest in Defense. Even when you invest in special defense, you aren't going to take very many hits from powerful special attackers with only base 70 special defense (like Mega Charizard Y, Blacephalon, etc). It would probably be better to invest in physical defense so that you can check powerful physical attackers better like Belly Drum Azumarill, Swords Dance Excadrill, Dragon Dance Mega Gyarados, Swift Swim Mega Swampert, etc.
Hope this helped!