They move all over till they settle down. I had one on an overflow for yrs with some of it always flowing through the teeth. Thought it was stuck in the teeth for a while but if I touched it it would pull itself right out and close up. Then open and go right back again
The rocks in the pics does not look like it has enough holes/caves to plant its foot into. They look more like base rocks. I'm just going by what I see in the pics. Try finding a rock with lots of wholes and big enough for it to settle into.
With it on the move make sure you have foam filters on your powerheads. One day I saw movement in my tank and watched my float from one side to the other in the flow and ended up tenticle first in the powerhead...luckily I'd put the foam on them after it got sucked in a month or so before.