San Francisco, the birthplace of street skateboarding, was also the first city to design solutions such as "pig's ears" — metal flanges added to the corner edges of pavements and low walls to deter skateboarders.

In 1999 the debate once again become a front burner issue when the city installed SkateBlocks, or "pig ears," as the police department calls them, on the raised concrete portions of the Ribbon.

Adding physical obstacles such as "pig ears" (metal clips installed on surfaces to impede skating) generally won't raise the possibility of a successful suit by an injured skater, Bates says, as long as the property warns them of known hazards.