Interesting I had no problem with Giraffe. In fact that's what was in this enclosure before the elephants, using the wood and they never broke it. Wonder if the Grade 2 is correct but there is a bug.Having the same problem. So annoying! Had it too with the girrafes. It's says grade 2 but they immediatly burst through it. Had to make it concrete...
I don’t know if this is helpful at all, but I noticed that animals get MAD if the fence welfare goes under 49%. No matter if the fence is perfect for them, the moment it gets a little used they will literally attack it again and again to tear it apart. I had this problem with elephants, bisons, giraffes and even antelopes.
For me, the solution was having a mechanic only working on fences to keep them well above green. I don’t know if it’s intended.