Ferrothorn is a very good wall for competitive battling. Here's what I recomend:
Ferrothorn@ leftovers
ability: iron barbs
EV's: 252 hp/ 80 def / 176 sp def
nature: +def -sp att or speed
moves:
stealth rock
power whip
leech seed
toxic/ thunder wave
you could also use:
curse
gyro ball
stealth rock
leech seed
If you would rather use Bronzong then this is what I recommend:
Bronzong@leftovers
ability: levitate
EV's: 252 hp/ 128 def/ 128 sp def
nature: +def or sp def -speed or sp att
moves:
stealth rock
confuse ray/ swagger
hypnosis/ toxic
zen headbutt/ earthquake/ payback/ gyro ball
Over all, I recommend Ferrothorn.
Hope this helps :)