Are you referring to Stun Blocks? Because if so, there is already anspell (Stun Block)available for all that caters for this.
Or are you just referring to a spell that gives the user two Tower Shields instead of one?
Neither. It would be a spell or a treasure card that when cast on an opponent would put two shield blocks on them so they could not shield for three rounds. The first time they tried to put a shield of any kind up one of the shield blocks would be destroyed and they would get no shiel(s). So they would have to shield 3 times to get a shield.
It would completely destroy PVP. How can a storm not shield with less than 5,000 Health at level 125. Two hits and the storm is dead. Maybe you should try to pvp and not shield, then tell us what happens.