My pond is leaking, and I've heard that duck poop is a good sealant. We get the occasional migrating pair, but the pond is small, so they're not comfortable to stay with dogs around. I have noticed that they eat more eggs than anything. I can have a good deposit of tadpole eggs in the shallows, but just one evening visit by a pair of Mallards will decimate the egg beds. Good cover will protect your fishery, IMO.
Geese are another issue - they poop on land and are not allowed in any way! They get shooed away by lead rain, and I do not mow the pond banks.
Cheers, -Hirsch
