Melanurus Wrasse - Worried about it moving old sand and causing death from gas?

So I have always wanted a Melanurus Wrasse and was talking to people at my LFS.



I know that they like to bury themselves in the Sand when they sleep or get stressed out.



But then again I have a Lot of Coral (Favia and Chalices) that cover my Sand Bed.



The person at the LFS said do not worry they won't bury themselves where there is a lot of Coral around.



He said they would just bury themselves behind my Live Rock.



At first I said OK Great.



Then I got scarred because I talked to somebody before that was moving his Rock Around and Re-Aquascaping.



Right after he did that everything got sick and some stuff died.



The LFS told him it was because some kind of Gas gets trapped in the Live Sand that you do not Vacuum on a Regular Basis and he stirred it up.



I only Vacuum My Sand in the Front and Sides of the Tank.



So then I thought oh God the same disaster will happen to me if I get this Wrasse.



But I really want one.



What are the odds that the same thing will happen to me that happened to the person I talked to?