If I understand correctly, you've used the maximum amount of vitamins on the stats you've listed? Well, I don't know if you know this, but that is not the maximum amount of evs that can be put into a stat; vitamins only raise a stat to a maxium of 100 evs, while you can raise that to an optimum amount of 252 by training. You can ev it however you want, but I would recommend the following ev spreads: 252 HP, 252 Def, and 4 Att. This set will serve you well as a defensive wall, as Aggron's base 180 defense is stellar. Another spread is 252 HP, 252 Att, and 4 Spd. This is a tank set, which can take many hits on the physical side and dish them out, and with the lax nature you'll be taking hits better at the cost of less power, since it's not an attack boosting nature. I would recommend that you remove the special defense evs completely, by means of the ev-reducing berries, as Aggron's base special defense is not good. Also, I would remove the defense evs if you're wanting to run a tank set, and if you do want defense investment with the tank set, you can put in about 16 or 32 evs in defense, by taking away from the HP evs, since you have a lax nature. So the spread could be 224 HP, 252 Att, 32 defense. Hope I helped!