I had a local rockpool set-up running but didn't have a chiller so had problems with heat over summer. I just went to the rock pools, gathered critters, rocks and water and took it all home and put it in a 3ft tank with an Aquaclear 500 filter.
Most interesting tank we ever had. It was stocked with shrimps, anemones, sea cucumbers, triplefins, rockfish, brittlestars, starfish, hermit crabs, chitons and anything else we could catch. Every so often I would top the tank up with fresh seawater and add some sea lettuce.