Lta's like the sand, or atleast next to something in the sand ime. Try not to hurt its foot (attaching/detaching from rocks will do it) or you may have difficulties getting it to anchor down at all.
Try a spot next to a rock with good light and flow, then let it move where it wants.
My lta took about a week to anchor down. I dug out some sand next to a rock and placed it in the hole. After it attached to the rock some I gently filled in the gaps with sand. It moved some atfirst, just readjusting itself/digging in.. since it hasnt moved (2 months or more).