"attaching" plants to side of pond

I have a pond with very narrow shelves that seem to slant down towards the
pond, so I have a very hard time keeping plants on the shelf (I've kept a
few there by putting a heavy rock in the pot on the higher part of the shelf
next to the pond wall). I've now got a couple of larger plants I want to
put in that I don't think the rock trick will be enough. I'm even
considered tying rope around the plant and attaching the ends under the rock
on the sides of the pond or maybe over the sides and into the ground.
I'm sure all you smart ponders out there probably have a more ingenious
method--I hope?
Thanks,
Kirsten