If you are using the base DK macro to figure out your avoidance with SSG vs. Swordshattering, then that macro returns false values for SSG. Try these for SSG:
Nightelf (Blood/Unholy Tank (No Frigid Dreadplate))
/run ChatFrame1:AddMessage(format("Avoidance with Stoneskin Gargoyle: %.2f%%", GetDodgeChance() + GetParryChance() + 8 + 1/(0.0625 + 0.956/(floor(GetCombatRatingBonus(CR_DEFENSE_SKILL))*0.04))))
Nightelf (Frost (or others specs with Frigid Dreadplate))
/run ChatFrame1:AddMessage(format("Avoidance with Stoneskin Gargoyle: %.2f%%", GetDodgeChance() + GetParryChance() + 11 + 1/(0.0625 + 0.956/(floor(GetCombatRatingBonus(CR_DEFENSE_SKILL))*0.04))))
All Other Races (Blood/Unholy (No Frigid Dreadplate))
/run ChatFrame1:AddMessage(format("Avoidance with Stoneskin Gargoyle: %.2f%%", GetDodgeChance() + GetParryChance() + 6 + 1/(0.0625 + 0.956/(floor(GetCombatRatingBonus(CR_DEFENSE_SKILL))*0.04))))
All Other Races (Frost (Or other specs with Frigid Dreadplate)
/run ChatFrame1:AddMessage(format("Avoidance with Stoneskin Gargoyle: %.2f%%", GetDodgeChance() + GetParryChance() + 9 + 1/(0.0625 + 0.956/(floor(GetCombatRatingBonus(CR_DEFENSE_SKILL))*0.04))))
These return post-DR avoidance, so they will be lower than if you actually added your dodge/parry/miss from your character sheet.
For the rest of you and those Dks not using SSG:
/script DEFAULT_CHAT_FRAME:AddMessage("Currently combined avoidance at:",0.8,0.8,1)
/script DEFAULT_CHAT_FRAME:AddMessage(GetDodgeChance()+GetParryChance()+5+(GetCombatRating(CR_DEFENSE_SKILL)*150/355)*0.04,1,0.5,0)
For NEs (Blood/Unholy Dk & Warrior)
/script DEFAULT_CHAT_FRAME:AddMessage("Currently combined avoidance at:",0.8,0.8,1)
/script DEFAULT_CHAT_FRAME:AddMessage(GetDodgeChance()+GetParryChance()+7+(GetCombatRating(CR_DEFENSE_SKILL)*150/355)*0.04,1,0.5,0)
For Frost NE (or other specs with frigid dreadplate)
/script DEFAULT_CHAT_FRAME:AddMessage("Currently combined avoidance at:",0.8,0.8,1)
/script DEFAULT_CHAT_FRAME:AddMessage(GetDodgeChance()+GetParryChance()+10+(GetCombatRating(CR_DEFENSE_SKILL)*150/355)*0.04,1,0.5,0)