Skatestopper

Skatestopper is a skate-deterrent device placed on urban terrain features such as benches and handrails to discourage skateboarding on the surfaces where they have been installed. The name Skatestopper is a registered trademark of Intellicept of El Cajon, California, but in some skateboarding circles it has become a genericized term referring to any anti-skate device.
The aim of skatestoppers is to stop skaters from practicing grinds on urban features such as curbs, benches, and ledges, which can damage those structures.
Criticism.
Some have viewed skatestoppers as just another obstacle to be overcome and the presence of skatestoppers actually encourages them to stay in the location longer.