Spring Street Park Playground is one of only two public spaces in Downtown Los Angeles set aside for children. Unfortunately, dogs have been entering the playground, creating a safety hazard for the young children who play there every day. Even "good" dogs can become aggressive when approached by young children, so it is essential for the safety of both dogs and children that the playground be kept a kids-only zone. A fence is a cost-effective measure that can prevent a tragedy and allow children and dogs to co-exist safely within Spring Street Park. 

ETA: It's been called to my attention that there are also problems with people who are high, drunk and/or mentally ill hanging out in the playground area. All the more reason to have a fence to control access to the playground.