Okay, lets begin
Swampert is one of the most solid defensive Pokemon in the whole game, he can guarantee stealth rocks, his typing gives him only one weakness (grass) which can easily be overshadowed if you have a correct team to back him up, one of my personal favorite tanks, anybody who underestimates him will find his team slowly crippled.
Next up is cradily, cradily is a beast in sandstorm, already high defense/special defense, curse makes cradily even bulkier, at the sacrifice of some of cradily's already poor speed, which isn't a big loss, furthermore, sandstorm increases cradily's special defense 50%, it becomes unstoppable, plus an instant recovery move (return)
But!, in order of this all to work your lead must be tyranitar, since he sets up a permanent sandstorm, its a team witch nobody will ever suspect.
And lastly Bronzong!
Bronzong is the best wall in the game, only one weakness, a Petunia of resistances, many of witch are common, bronzong makes a fantastic support pokemon, but to make bronzong even stronger, teach wish to blissey, as it will help him recover some HP
Hope i helped :]