OK....the one that is the biggest problem at the moment is in a
"companion planter"....I've moved most of the plants into planters that
take groups of three.....I've put rocks on the top of the soil....I now
have rocks on the bottom of the pond....

I guess the answer is to move the one, still misbehaving planter to a
more sheltered part of the pond and look at the sack planters and
filling them with rocks and soil before attempting replanting that
specific area.....

Thanks to everyone for your responses
Gill