Among potential Special options for countering Gallade, Acid Spray is one of the ones to worry about. Your Sp.Def getting halved in one hit ruins any Focus Sash potential (unlikely) and decreases Gallade's ability to Special Wall. Few Pokemon have the Sp.Atk to use Acid Spray properly, but Tentacruel, Accelgor, and Octillery have the best potential. However, all 3 have issues against Gallade's offense:
-Accel' fears getting hit in-general* and can only neutral-hit Gallade
-Octillery needs Trick Room to outrun Gallade, is easily handled by either Thunderpunch or Leaf Blade, and is only-slightly-less of a glass cannon than Rampardos
-'cruel has low Defense, slightly-above-average Sp.Atk, and is handled by either Thunderpunch or Bulldoze/EQ
-All 3 may only get a single shot in if they have to switch into Gallade