Have you tried seating your potted plant into another larger vessel or basket? You could fill in the air space with anything from styro peanuts, to CH fiber, to pebbles.
I poke in some spanish moss around mine when they're seated in larger cache pots (just around the tops), ends up looking rather pretty.
Thanks for the tips - but mine actually moves in the hydroleca I use - as I may have said elsewhere it is very very lightweight even when wet and I gave the poor plant a very drastic root pruning at the repotting stage. I might try a new pot and bury the new roots that are already used to S/H a bit deeper in it.