HELP! natural pond and coop!

[chickenz101]

I have two ducklings at the moment that one day will live on my natural pond. But I'm worried about foxes and them getting away. A stream runs through the pond and I can't block it up. I can't afford to get tall fencing the whole way round. It is quite overgrown with pond plants and there is also alot of grass around! What can I do to secure them, and keep the fox away? Any help would be appreciated and if anyone had the same problem. Btw I live in England!