The best offense is a good offense. I mean defense, or however they say it. Anyway, two shields!

Shield Slam

Starting at 3rd level, when wearing a shield, you can use your shield to make a slam attack as a bonus action in the same manner as someone wielding two light weapons. Additionally, you gain the benefit of the Two-Weapon Fighting style feat when using your shield slam, allowing you to add your Strength modifier to the damage roll. Your shield slam deals 1d6 bludgeoning damage, plus your Strength modifier. Making a slam attack in this way means you lose the bonus that your shield grants to AC until the start of your next turn.

Nimbly Amored

From 7th level and on, when wearing heavy armor you can add your Dexterity modifier (maximum +2) to your AC, as if you were wearing medium armor.

Reflexive Cover

Raising your shield is second nature and comes as easily as breathing. Beginning at 7th level,  you can now add the bonus to armor class from one shield to all Dexterity saving throws you make. This bonus to Dexterity saving throws does not increase when you gain the Dual Shields ability at level 10 in the subclass.

Shield Throw

At 7th level, you can use your shield as a thrown weapon with a range of 20ft (50ft). The damage for this is the same as your shield slam.

Dual Shields

Your dedication to the art of the shield has taught you how to truly master shields. When you attain 10th level, you can wear two shields and gain a bonus to your Armor Class from both. Additionally, you can now shield slam for every attack on your turn. Both shields count as light weapons, allowing you to take a bonus action to slam again, as with the 3rd level ability. Shield slamming in this way means you lose the bonus to AC from only one of your shields until the start of your next turn.

Shield Wall of One

Beginning at level 10, your shields no longer protect just you. As long as you are wearing and benefiting from at least one shield, all allies in an adjacent square to you gain a +1 bonus to their AC and Dexterity saving throws. Your allies lose this benefit if you are incapacitated.

You may spend a reaction to increase the bonus to +2 for one adjacent ally. This increase lasts until the start of your next turn. You may do this a number of times equal to your proficiency bonus. You regain all expended uses after a long rest.

Returning Shield

From 15th level and on, when you throw your shield inside its normal range, it will ricochet back to you at the start of your next turn. Catching it takes no action. Your shield cannot return to you if the path back to you is blocked, such as a closed door. Half Cover may potentially block the shield's path, depending on DM discretion. Three-Quarters Cover and Total Cover will always block the shield's path.

Turtled Up

At 18th level, you are able to hide behind your shields to amazing effect. If you are wearing two shields, and as long as you are aware of your attacker and not incapacitated or surprised, you are immune to all nonmagical ranged attacks.