Tip from another
"1. Shooting through fences
One of the big challenges at a zoo is to clear the fence and, for the sportier ones amongst you, that doesn't mean jumping over it. Animals in cages tend to be surrounded by a fine wire mesh that often rises above eye level. So you often have to take photos with the cage in front of you. If you don't adjust the camera's settings and position you will have poor photos with a blurred grid. To compensate you need to move as close as possible to the fence. Position the camera so the lens is pointing through one of the gaps or, when the fence has small gaps, make sure that the face of the animal you're photographing is in a gap.
If the camera has manual exposure control, adjust the aperture so it's at a wider setting, this will reduce depth-of-field (front to back sharpness) and throw the fence out of focus. Hopefully the fence will be so blurred it won't be seen in the photo.
If you can't shoot through or throw the fence out of focus you can often clone it out later using an image editing program. "
Hope that helped.. I always just did the maneuvering till I got the animal right inside a square in the fence and shot through it. Fencing is always an issue at the zoo (along with glass)..