Business owners on Auto Row aren't taking any chances. But sometimes even the boards don't help.
"There're some boards that were on it just to prevent damage that were yanked off," said building owner Martin Kaufman. "And unfortunately there was some further damage done."
Kaufman's building was one of many damaged in Friday night's march. It's one that began peacefully, but then took a turn for the worse.
"A very small group of people with rocks in their pockets and malice in their hearts disturbed what was otherwise a very positive day in Oakland," said Mayor Libby Schaaf.
The mayor and police chief spoke at a Saturday morning press conference.
PHOTOS: Cars burned, windows smashed in Oakland protest
Indeed, organizers of the May Day march against police violence say the vandals weren't with them.
"We don't know who those people are and they're not linked with us at all, period," said Shonda Roberts with the East Bay Organizing Committee.
When she's not marching, Roberts works at a KFC that was heavily damaged amid the chaos.
"I don't want to see my community look like this," she said. "I don't want to see my job, my workplace look like this, you know? And you have to explain to your customers what's going on and that's what we've been doing all day."
Perhaps the worst destruction was at a Hyundai dealership. More than 50 brand new cars were vandalized, some beyond repair. Neighbors came down to look.
"Doesn't make any sense," said one neighbor. "It improves nothing and we get nothing from the vandalism except a bad looking neighborhood."
Police admit they could have done better.
"We do feel we did a good job yesterday as far as protecting human life," said Police Chief Sean Whent. "However, obviously it did not go well in terms of protecting property."
Public Works crews have been out helping merchants clean up.
"Graffiti, glass cleanup, things like that," said an official with Oakland's Public Works Agency. "We'll be helping with that, any litter, anything that they need."
And though police have made 12 arrests, they're asking the public for any video of the march that could help them identify more suspects.