A California grassroots protest group had a flash of inspiration: Members would scurry onto an open space near Donald Trump’s National Golf Course in Rancho Palos Verdes and arrange themselves to spell out “RESIST!”

The Saturday action by Indivisible San Pedro — whose members sometimes refer to themselves as “The Indivisibles” — went off without a hitch. Los Angeles County sheriff’s deputies showed up, but the protest was peaceful and broke no laws. While the 30-foot-tall “letters” look like they’re in the center of Trump’s coastal golf course — and close to the clubhouse — they were actually created by some 200 protesters in a small park that’s part of the grounds.

Retired journalist and Indivisible group member Peter Warren told HuffPost the flash-mob action was something creative and effective the organization could pull off quickly without any funds — though it took a major investment of volunteer hours. Members planned the strike to be lightning-fast. “We wanted an element of surprise,” he said. “By the time the Trump people figured out what we were doing, we’d be gone.”

The group studied public access and parking, and learned they didn’t need a permit for their protest. They met with a member of the Coastal Commission who told them they absolutely had a First Amendment right to protest at the spot, said Warren.

Theater professional and group member Melanie Jones planned out most of the logistics, said Warren. She calculated how many people — two deep and lying down — it would take to make each letter “tall” enough to be easily filmed by a drone arranged for the event. The group practiced once forming the letter “T” during a weekly meetings.

Participants were told to be at the site at 9 a.m. and wearing white. They gathered at different picnic tables to meet with their specific “letter captain.” The entire letter-creating operation took about 15 minutes, and people sang “God Bless America” as they lay in their human “Resist” message, Warren said. Then they were out of there.

“We had a good time,” said Warren.

Protesters were calling for a special prosecutor to be named to investigate Russian interference in the presidential election and any Russian connection to the Trump administration. Indivisible San Pedro also called for Trump to release his tax returns.