Lots of barb-wire protecting a historic Cemetery in the middle of San Francisco, CA

We do not know the details and reason for this protective measure. The wall around the cemetery
is heavily fortified by a fence with barb wire atop of it. Gravediggers? Trespassers? Graffiti vandals?
I think it is sad that such measures are needed in this City. Thousands of historic
cemeteries are across Europe, you will not see a barb wire fence there anyplace.