GTS,
I feel ur anger on the cats. I hate cats as well but if you do anything hasty like killing the cats you will just get in trouble.
Well, first of all where in FL are you. Actually Rayman's joke suggestion of gators is a possibility. If you love gators that is. I heard that FL residents can apply for a licnese to keep gators for $50 I heard. So if the cats so happen to get eaten by your pet gator, it's not your problem as the gator was in your pond and in your property.
What I do usually to the cat in my yards is I trap them. Then I bring them to the animalm shelter. If the cat is tagged they will contact the owner and she will come and have to pay a fee before she can pick up the cat. If she has 20 cats and say the bill is $50 per cat. That is $1000 she will be spending if you turn in all her 20 cats. LOL! But IMO I like the gator idea better.
But if you really dont want a gator, I suggest electric fencing. My friend has it around his pond here and it's "roasted" a couple squierels here and there. But that wont keep the cats out of your property. That will just keep them out of the pond. Trap them and turn them in or trap them and throw them to a gator you see in the canals. LOL!