The method of total protection from dilution is called a full ratchet and ensures that should a fundraising round cause a previous investor’s ownership percentage to decrease as a result of newly issued shares, they will be given the opportunity to maintain their ownership level.
In more technical terms, it is a type of Antidilution Protection that adjusts the Conversion Ratio so that each share of Preferred Stock will be convertible into a number of shares of Common Stock equal to the number of shares the investor would have received, if the investor had purchased the shares at the lowest subsequent price at which the company later sells its stock. The number of shares sold at the lower price doesn’t matter. Only the lower price matters. For example, if the company sells Preferred Stock with a one-for-one Conversion Ratio for $10 per share and later sells Common Stock for $1 per share, each share of Preferred Stock would become convertible into ten shares of Common Stock, even if only one share is sold at the lower price.