Bunny Content Blocker

Does anyone know how to get a content blocker for the computer that will keep the bunnies from accessing sites like that gardening board that keeps giving them the worst ideas possible? I've found plenty of programs to block x-rated stuff for kids, but nothing that provides appropriate protection for rabbits. The food co-op has a frightening selection of loose herbs, and the bunnies are looking some of those up now to see which might be easy to start from the loose mix, so I need a good blocker fast.