Absol is generally all about power, and you should not be concerned about its defenses, because they're actually quite bad. Rather than beef up Absol's defenses, take advantage of the fact that Ansol can have teammates that can help sponge any unnecessary damage, and use Absol to sweep the rest of the team. Use defensive Pokemon with some form of recovery to heal off residual damage. For example, Gliscor deals with absol's Bug and Fighting weakness. In addition, you could set up Light Screen and Reflect to halve damage from attacks.
Mega Absol should be running a Swords Dance set, or an all out attacking set.
Normal Absol's Life Orb all out attacking set stands out most of all.