Oh Okay, I'll shoot close to the fence. The zoo or animal theme park is the only way I can shoot tigers and lions. Unless, I travel to China or Africa. It is not too bad to shoot animals through the fence. It just give the feeling that they are in the cage.
For the fence to disappear, you need to be close to it, but also the subject needs to be far from it... I would say about 8ft,at least.
If the animal is too close to the fence, I don't think you'll be able to make it disappear.