Shields X: A cumulative, static ability that means, "The attacking unit gets –X power against this unit." Shields only matters when attack dice are rolled. If you give a unit Shields after your opponent has rolled for damage, it doesn't affect the roll.
Persuade
Persuade X: An activated ability that means, "Prevent up to X damage to this unit, and the attacking unit, if any, loses power for its next attack equal to the amount of damage prevented this way."