Landorus-T has no solid counters. Whilst a number of things may be able to wall the common Earthquake/Stone Edge/U-turn set, it has a number of tricks up its sleeves that enable it to bypass any potential check. With Gravity, it can turn the tables on Bronzong/Skarmory, and with enough Sp. Attack to make viable use of Hidden Power [Ice], even Gliscor and Tangrowth can't switch in with impunity. Hell, it can even use Bulk Up to let it survive Ice Shards from things like Mamoswine.
I'd say perhaps the most reliable check to Landorus-T in general would be Bold Cresselia, as it takes less than 33% from U-turn from the standard Stealth Rock pivot set, whilst being able to comfortably 2HKO it with Ice Beam and recover off any damage with Moonlight. If we're just talking pure physical sets, then Tangrowth/your own Landorus-T with HP [Ice]/Gliscor with Ice Fang are able to take it on solidly, as can Bronzong if the enemy Landorus-T does not have Gravity. Skarmory, whilst not being able to threaten it directly, can at least force out the double dance sets with Whirlwind.
As Neliel has already mentioned, perhaps Landorus-T's downfall are weaknesses to common moves, coupled with its average but acceptable base Speed. The key to beating it successfully is to keep it under offensive pressure - as long as you don't let it set up, you should have little problem revenge killing it. You don't necessarily need to use a Water/Ice attack to KO it - in general it struggles to take strong special attacks.