Hundreds of Thumbtacks Found in California Dog Park

— -- Hundreds of thumbtacks have been found strewn across a California dog park on multiple occasions, apparently placed there intentionally to harm the pets that play in the park, police told ABC owned station KGO in San Francisco.

Dog owners began to notice the dangerous tacks at the Ohlone Dog Park in Hercules last month and collected enough to fill several sandwich bags, KGO reported. But when they returned, more tacks had appeared.

"After we've gotten most of them out, then we come back and they're back again," Bay Area dog owner Annie Miller told KGO.

At least two dogs have been hurt from the tacks, according to witnesses.

"One of the guys was picking them up and his dog swallowed one and he had to take him to the vet," Miller said. "I'm sure it's not a very nice vet bill."

"Another person, their dog was limping and she put the paw up and there was a tack, not all the way in, but it was in the paw," dog owner Kathy Long told KGO.

Police said animals aren't the only ones in danger, as the thumbtacks could be harmful to children as well, since they're small enough to swallow.

"A child is very quick with that kind of thing and could have it in his mouth and swallow it before any parent could reach them," said Connie Van Putten, public information officer for the Hercules Police Department.

Police are asking the public to report any suspicious activity in the area.