Yes, mesh works but it looks awful. Depending on the size of your pond, it may be worth considering the edges surrounding the pool.
If you make it impossible for a heron to stand on the side by building up with boulders and planting in beween with stiff bush/plants to ensure an very uneven surround where they can't stand on the side for their fishing. That is ofcourse assuming that your pond is deeper than the heron's wading maximum.
If you have a fairly small pool you could make/buy a piece of welded mesh justa bit smaller than the pond size/shape, preferably made of aluminium, and paint that green - again, powdercoating that will make it last for many years. This mesh needs to fit a couple of inches under the surface of the water and will be very hard to notice. To make it easier for the fish to swim to the top consideration must be given to the size of the fish in relation to the mesh. Having a 'step up' about 1' from the edge right around will enable you to have the mesh only big enough as the hight of the fish as they will be able to swim horizontally through the mesh. It is a lot of work, I know. But it all depends on how natural you want the pond to look.