People might be using the wrong move against it, then:I've mentioned Qwilfish before and its been doing pretty good at walling other Azumarills. Tentacruel is OK, but its defence is not as good and Qwil has both better Defence and Intimidate to soften the blows.
+6 252+ Atk Huge Power Azumarill (Move 4) vs. 252 HP / 204+ Def Qwilfish: 97 - 114.07%
(Move 4) is Play Rough, modeled as Poison for Qwilfish's resistances. Azumarill was also modeled as Water/Poison for STAB purposes. After SR, that's a guaranteed OHKO, and even without it, chances are pretty high.