you can change how much damage a unit takes by using a damage engine which modifies the damage based on something you specify for example the wc3 damage reduction formula for armor is ((armor)*0.06)/(1+0.06*(armor)) - this gives an ever decreasing amount of reduction per armor point, what you could do is write
damage = damage - (((sqrt(strength))*0.06)/(1+0.06*(sqrt(strength))) * damage) -- so for example a unit will be hit for 100 damage and he has 100 strength then he will only take 100 - (10*0.06/1+0.06*10 * 100)= 62.5 damage
however this way the amount of reduction will not be displayed anywhere and there is no way to display it unless you use some kind of lame texttag somewhere