Shooting through a Cage and Glass
A lot of wildlife parks keep their animals in open mesh cages. You can make the cage literally disappear by pressing your lens against the mesh (rubber lens hoods or skylight filters are great for making sure the lens is not damaged in the process!), making sure your lens is positioned so the wire of the cage is not in the centre of the frame, and setting an
aperture of f/5.6 or f/8. Then focus on your subject and shoot.
This picture of the Scottish Wildcat was taken in this way using a 100mm lens at f/5.6. These rare wild cats look tame but have been known to bite through the steel and leather protective gloves used by the keepers!