Ask any one-legged surfer and I'm sure they'll tell you swimming with sharks might never be a good idea. But still, the Remote Controlled Robotic Shark should be a safe aquatic companion. The shark is 2 feet long, costs $100, and has a full range of motion to replicate the sleek (and demonic) swimming of nature's least-affable predator. It can swim to depths up to 9 feet and can venture up to 40 feet out from its fully submersible handheld remote. Just don't plan any lengthy oceanic sojourns with your razor-toothed friend; the shark's battery has only a 15-minute run time per charge. Nonetheless, it should help make beach trips less about sandcastles and more about getting swimmers to soil their trunks.
Remote Controlled Robot Shark, via The Red Ferret Journal