Risky Method

Before coming to an answer, Huang Xun started to quickly recall all those previous adventures she and Dai had undergone. 

In those times, they were either accompanied by an expert or fully showcased their identities. Both times, they had secure protections. 

The expert guarding them was self-explanatory.

But even without an expert, nobody would dare to even attempt to assassinate them. 

As they and many other Holy Lands or Holy Martial Families have life-crystals attached to their souls.

If they were dead, in a long period of unconsciousness, or unable to use their Inner World, the life-crystal would alert the other line no matter what. 

And once this happens, the consequences for the opposing force would be unthinkable.

The only known counter to this is to have a high enough cultivation to completely erase the soul and the life-crystal, preventing information leaking.