Important Note:I have not tested this technique out myself, I'm just putting it out there as a theory.
RIOT SHIELD
Shields are great. They block all damage going towards you, and even have other uses such as shield cancelling and shield bumping. The only downside to shielding all the time is that you're never going to hit anything because you can't attack while you're using a shield.
OR CAN YOU?
Behold, the Riot Shield technique!
It consists of two party members, one being the riot shield and one as the gunner. The riot shield would be a sort of "tank" archetype, with high defense armour and shields. For this role, disregard any attack debuffs as you're not going to be attacking.
The second party member is the gunner. They just need to have guns, or other long range weapons (say, a winmillion). Defensive weaknesses are unimportant, because if you do this correctly, you won't get hit.
Here's the key part. The gunner stands behind the riot shield, while the riot shield simply shields and stays between the gunner and the enemies. Whether this would work if the gunner just stood directly on top of the riot shield I do not know, as I'm just the theorist not the tester.
In a combat situation, the gunner hides behind the riot shield and shoots at the monsters while at the same time being completely safe from attack. If an enemy does get uncomfortably close, the riot shield shield bumps them away. The riot shield just stays there, shielding.
Well there you have it! If you try this out I would love to hear your results and if this actually does work or not.
It's an interesting idea, and I've thought about it myself as well. In the practical sense though, I don't think it's nearly as fast or as easy than going without a riot shield. I'm sure most experienced gunners would be able to weave and dodge through most mobs without taking any damage. The shield itself would most likely break within seconds if it were to take so many hits, and not to mention monsters would just switch their aggro to the player who is dealing damage. As for whether it would work if the gunner stands in the same place as the shield, I think both would take damage from an attack. Monster attacks deal damage to all knights in line of fire, so you can throw yourself in between a homming Howlizter and your team mate to tank the hit for them with your shield.
Something to try along those lines would be having the two players play in a tag-team style where they switch in and out so that both shields are used instead of just one taking all the damage.