Well I'm not sure about the vialibity of Counter. If you wanted to use a support/wall Aggron i'd probably use a set like
Aggron @ Leftovers
EVs: 252 HP/ 4 Def/ 252 SpD
Nature: Relaxed (Since this is what you have :c)
~ Metal Burst (Counter in this case)
~ Stealth Rock
Metal Burst + Sturdy + Taunt would basically kill everything, but unfortunately you only have Counter (if you can replace it that'll be awesome) you'll have to stick with that and hope that you get physical attacked :P I'd would preferably run a +SpD nature but meh. You can change it to full defensive due to Counter so 252 HP/ 252 Def/ 4 SpD
Stealth Rock is for hazards and Roar is to do some phazing.
However... you could try running Earthquake/Stealth Rock/Toxic with Counter, toxic hiting everything apart from steel types with poison, Earthquake taking care of the Steel types, Stealth rocks for the obvious setup.