A trebuchet is a classic device for throwing rocks (in your case sponges) at an enemy catapult. It consists of a long pivoted arm  with a sling at one end and a counterweight at the other. From the kit provided build a replica 'trebuchet' and several mobile defence shields. Once complete the clock starts and each team has to catapult their store of soaked-sponges into the opposition's territory. Only your shields can be used to block the incoming sponges. How many sponges will you be left with in your territory?