Ok, maybe this is common knowledge maybe not but here's a quick run through in tanking in ffbe.

There are two types of tanks: Cover and Provoke.

Cover works when the enemy attack some one else and your tank comes and cover the unit with enhanced defense. In the rumored future there is a tank that can cover the entire party.

Provoke changes the AI of the enemy so they will attack the tank more likely. Also in the rumored future, provoke tanks gets enhanced defense when provoking (Wilhelm, EV?, LMS). Also, there are special event items like the producer jacket and red nose that can push units with innate provoke to 100% provoke. (Guy).

Strategies I have seen people put golem on their Cecil and use provoke. This is a inefficient strategy, since Cecil is a cover tank, and it doesn't activate his saint wall. One trick you can do is get a 100% provoke unit (noctis, guy with golem provoke) and get Cecil to guard. There is a high chance cecil will cover the provoke unit and defends with a guarded cover defense (-75% damage reduction). This takes two units to do but doesn't require great gear to set up.

Provoke tanks can be by themselves but you need pretty good gear on them to make it work.

Keep these strategies in mind when ultros come. I was redoing ultros for fun on JP and he still hits pretty hard.