In our case, we have a physical fence (16' cattle panels on T-poles) that encloses a huge yard - probably close to an acre - and the pond. I'm looking for a non-physical barrier to keep the dog out of the pond, unless we allow her to take a dip. Even then, I'm a little nervous about that because of the possibility of water moccasins. I've seen at least one black snake, but I don't know if it's a water moccasin or not.
The invisible fence seems like a perfect solution (and probably cheaper) than more cattle panels, concrete, T-posts, and gates that we'd need to enclose just the pond.