You can avoid a natural 1 only if you are a Rogue level 11+, when all your rolls are at least 10.
However if you have a Halfling with the specific boost spell Improve Attribute, for Dexterity its called Cats Grace, your chance for a natural 1 is 1:(20 ^ 4) = 1:160,000.
Non-Halflings only get to 1:(20^2) = 1:400, so for them its a 0.25% chance.
