@FunkyGibbon I agree, these gabions (metal cages that usually used to be filled with rocks or gravel in civil engineering and landscaping) are not an ideal fence material as they essentially result in a double fence that isn't very easy to see (or photograph) through.
Given that Zie-Zoo is a small zoo they probably use building materials they can get easily in large quantities and for an affordable price tag.
Luckily the spotted hyena exhibit also has a part that is dry-moated and allows better viewing. But I still think it is a pretty good exhibit for a large predator living in a savanna environment.
Also, the hyena pictures I posted were actually taken through the gabion fencing, so it is not impossible either.
I didn't know that's what they were called
Assuming they were donated for free by a building firm or similar then it is a good use for them. I wonder if the dry moat also uses them in its construction?