My long tentacle keeps his foot buried in the sand at the base of a rock. Even so, he's pulled up twice. Once I thought he was going to flat out disintegrate he looked so bad, and then last time he just seemed to want to pull up stakes and float around a while. He did get caught in the intake of my HOB
protein skimmer, but I was able to unplug it and then pull out the strainer until he let go. Every time he's ended up prety close to the same spot. I've had some success with taking bits of live rock to make a coral around the foot. It seemto offer some protection from the current, but it's no guarantee.
. . .and right after he got caught in the protein skimmer intake: