Who loves stoneclaw totem / searing totem?

Srsly.

Tremor does nothing in my experience for the boss sleep from Eranikus. Grounding works but not tremor.

In fact, I even checked on wowhead for you:
I originally posted saying that a Shaman's Tremor Totem would be effective in preventing the sleep effect from Eranikus. However, it would seem it's not a "true" sleep effect, and so isn't affected by that totem.

Despite this, a Shaman is still a great asset on this fight, because Grounding Totem will absorb every sleep so long as it is active (WoWWiki points out that he uses no other single-target spells).

Start out with stoneclaw totem on Eranikus. Hopefully he'll "sleep" the totem, which is immune and will continue to pulse. You can even put tranquil air down to help keep the aggro on stoneclaw if it lives long enough. Of course, stoneclaw only has so much HP and you have to watch your aggro, but it will give you some lead time to whiddle away his health without worrying about a slept tank.

Then righteous defense+judge righteousness with your pally. Grounding totem the next sleep. BoP/Iceblock whoever he goes after and regain aggro (either by righteous defense + judge righteousness, or by throwing your captain america shield). Rinse, repeat. Between grounding, BoP, iceblock you should always have at least one ability ready to get the sleeps. You can also experiment with earthbind kiting if he's not immune to snares (I can't remember) while the pally is slept.

The key to this fight is watching your aggro like a hawk. Don't be afraid to stop DPS while your pally re-establishes aggro. They're good at frontloading.