If you call the people who will be insuring you, they will probably give you weekend coverage for a reasonable rate.
Sometimes you can also get onto a festival or organization rider clause for little expense too. If it's the council who want it try them.
The other tack would be to get some yellow "danger" tape, some big warning signs and make everyone watching sign a waiver. That might be worth doing even if you get the insurance.
Good Luck, JohnB