PJ,

I've always had cows with ponds and have never had any problems. I do fence them out of the pond which provides the fish for the table, however. Seems like it wouldn't be too difficult to make a lane for the cows to use for watering purposes. That fence would have to extend into the pond however, to be effective and that might limit your ability to easily move around the pond. A siphon system attached to an automatic float value external to the pond might be a better approach for watering livestock. Maybe someone has tried that?