Donphan's already been mentioned, and other bulky ground types can be just as troublesome with your lack of ground resists. There's a few others like Rhydon/Rhyperior and Hippowdon can even set up Swords Dances and Curses to sweep you rather than just relying on item boosts and supereffective stab.... But I don't need to go too much into that.
What I actually wanted to point out was the lack of water resists. Chandelure's Energy Ball is a mere 2HKO on bulky waters not 4x weak to it (even Azumarill at a mere 100/80/80 and max HP can take it without any hazard damage), making it easy for something like Nasty Plot Slowking to come in after a kill, obtain a boost and shred your team to bits. A grass-type could remedy this - depending on how comfortable you are using fast(ish) pokes under Trick Room, Celebi and Shaymin are good. Rotom-C or Tangrowth if you want something a little slower. Rotom-W might not be Grass-type, but it has the water resist and supereffective stab to hit them... all of the pokes mentioned can help with your ground type issues too.
Actually, Rhyperior isn't much of a problem because outside of Trick Room Chandelure OHKOs it with Energy Ball.
Now Hippowdon can be troublesome, but then again, it can't take special hits from Reuniculus and Uni won't be KO'd with a boosted EQ. (Thanks to it's bulk)
But yes a Ground/Water resistant wall is needed. You may want to go for Slowbro to hit Ground types hard while walling Waters. However, Rotom-W is VERY effective in not only countering both types, but Pokes that abuse moves with the above types.
For a defensive core, I suggest this Rotom-W
Rotom-W @Leftovers
Sassy (+SpDef -Spd), 252 HP/112 Def/144 SpDef/4 SpA
-Will-o-Wisp
-Hydro Pump
-Thunderbolt/HP Fire
-Rest/Pain Split
Bulky Rotom that covers your weaknesses, especially it's nice ability to check both physical and special attacking threats (bar Guts abusers)
You may want some more SpA EVs for a faster(lol?) and more effective attacker. Still, this Rotom works great even outside TR.
T-bolt over HP Fire because you already have some nice Ferrothorn counters..
You might want to consider Cresselia too. Although it doesn't resist Water, it has some gimmicks that could stall bulky ones out
Cresselia(F) @Leftovers
Sassy, Levitate
Max HP, Max Def, 4 SpA
-Calm Mind
-Psychic
-Ice Beam
-Rest/Moonlight
or
Cresselia(F) @Burn Orb
Sassy/Calm, Levitate
Max HP, 100 Def, 156 SpDef
-Psycho Shift
-Rest
-Sleep Talk/Psychic
-Ice Beam
You could swap it with Reuniculus and utilize a CM Cress with the first set, or a cool double status inducing Cress on the second set.
Let me explain how Psycho Shift Cress works
1. Cress gets burned by Burn Orb
2. Psycho Shift passes Cress's status onto the opponent, thus the opponent gets burned
3. You can use Ice Beam or Rest expecting a switch
4. Sleep Talk (If you have it) and pass your Sleep status(!!) when you activate Psycho Shift.
I've used both Pokes, and they both work fine despite their average Speeds. PsychoShift Cress gives you a nifty condition whereas you can control status, switch into the appropriate poke (ex: Rampardos) and clean up the fields. (btw PS Cress is a custom set made by me :D just saying)
There are many other Pokemon you could use as defensive counters, but try and find the most effective ones.