Davida1968
When we had cats, we placed various items (e.g. planted-up garden tubs, little garden ornaments) at points around our pond, in a strategic manner, so that out cats couldn't access the edges and dip their paws in. Also made we sure that the cats stayed inside the house at dusk and all night. It depends on how far you are willing to go, to keep the felines in check!
We did the same! We no longer have a cat, but do have visits from a neighbour's cat, who is quite keen to catch the birds. I watched him/her one day to see if there was a strategy that s/he used in the hopes that I could thwart the cat.
There were a couple of hiding places in particular flowerbeds, so I put various obstacles (tubs, filled watering cans etc) in the way, so the cat had to take a longer way round to reach the bird bath. It delayed it enough for the birds to see the cat and have time to escape. So far!!!