Thank you. 
I wasn’t sure it if worked like that or was something like it just subtracted 10% every stack or not.
I.E. -10% at 100 defense would be 90 then it would subtract another -10% making it 81
If your correct and it’s not, then it’s pretty dangerous. Also getting C2 Deeds of Valor 10 would mean having 0 defense at max stacks. 
Deeds of valor lvl 10
Attack per stack :10%
Defense per stack :-10%
Maximum stack :10
I think its mechanics work like this
1000 damage +10%+10%+10%+10%+10%+10%+10%+10%+10%+10%=?
1000+100+110+121+133.1+146.41+161+177+198.8+214.3+235=2593
Defense mechanic also similar i think
100% defense lost is nothing you just got extra 1593 damage,monster will die in second.
Trick to get 10 stack is pretty tricky,learn to use shield block(press C)if ur peltasta or Two handed sword block with highlander while kiting(taking damage)Bring potion lvl 10 or cleric/priest for ez stacking Deeds of valor.
If you bring priest with lvl 10 revive stacking Deeds of valor is like a breeze
Doopple c2 best partner is linker c2 and priest c3 = 10-15 min high tier dungeon lel
after you get 10 stacks use cyclone and then you will like HaHa.
Hopely dopple c3 will have defense -5% or 7% each stack.Defense attribute for Deeds of Valor lvl 15