Marc Savignac’s cottage north of Sudbury, Ont., has plenty of waterfront, but it’s too shallow for some of the fun stuff his kids wanted to do, such as having a rope swing into the lake. To compensate, he bought a water trampoline, but it didn’t deliver the bounce that it promised. The kids mostly used it for lounging. “They looked like a bunch of walruses sunning on an ice floe,” says Marc. “I thought, I have to do better than this.”