You need to put a rigid mesh over your pond that is too small for the ducks to reach through.The stuff for aviaries or pet runs should do. I bought a 10mx1m roll from a large DIY retailer a few years ago. Soft net could get caught up in the duck's feet or bill. Also look into bird scaring techniques, like hanging old CD's on strings - if you make your pond too noisy/busy the ducks will go elsewhere. Good luck.
Many thanks,showcatbeng,- I must admit I was thinking of trying a soft net but realise now that it could prove harmful. Like many I have lots of disgarded CDs and will give that a go.
Whilst I agree with Bellringers remark, goosander and merganser do eat fish and are ducks.
Extremely unlikely to get one of them on your garden pond though.
Another thing is, the ducks may eat up any unsightly duck weed on your pond perhaps.
Have you actually seen ducks on your pond?
Thanks Bellringer and Avatar. Yes, we have had a pair visiting our pond on and off for the last few days. We've checked and they are Mallards. We have also seen some of our fish since they have turned up. So, we can rest easy it seems - except for the smelly excrement on our lawn ! All advice has been appreciated.