if the frag is closer then 2 1/2" to the glass my turbos will knock it down, like wise it cant be that close to a rock either. i have a good amount of nass and tongan nass snails in the tank, so i have seen them come up and slightly uproot it.
my powder brown has his "lanes" that he likes to run and if the frags are tall enough he will knock them over.
after awhile i picked the current spot they are all in only my largest turbo can knock them over so its not often i have to put them right side up.
i took out my biggest offender of coral moving months ago, my GSM. he would pick up my new frags for the first couple of days and drop them in random places, letting me know it was his tank.
after he killed my long tentacle plate he was banished to the sump untill i found someone to take him.