Clad in a custom-made orange-and-green wet suit, he sits calmly on his board among the other surfers, waiting for a swell. Spotting a wave, he jumps up. Moments later, perfectly balanced, eyes on the beach, nose to the wind, he's sittin' on top of the world. Even in a sport known for its hot-doggers, Rocky, age 8, stands out: He's the one with four feet.

A former stray, Rocky belongs to Robin Marien, 29, a San Diego construction worker, and his wife, Michelle, 28, a chemical engineer. Robin found Rocky when the pup was 3 months old and wandering forlornly around a Department of Motor Vehicles parking lot. "It was about 110 degrees out," says Robin. "Poor dog's tongue was hanging out. He was in bad shape, so I took him home."

Three years later, Marien remembers, "I was pulling my board along the shoreline. All of a sudden I looked back and saw that Rocky was standing on it. I figured, okay, what the hell, if that's what he wants. So I took him out, let him go, and he caught the wave the very first time."

The versatile Rocky not only rides atop his own double-finned boogie board, he also cruises with one of Robin's buddies astride the nose of a nine-foot surfboard. On shore, he retrieves his board with his teeth. He chews through three or four a year. Rocky, who as near as anyone can determine is part shelty, also water-skis and wind-surfs. "At times I think he might not really be a dog," says Marien, who helps Rocky by lining him up with the waves. "I think maybe he's really a seal."

Just in case, Rocky wears a specially fitted wet suit with buoys to bring him quickly to the surface after a dive. "Sometimes when he goes under and is tumbling around in the soup for more than 15 seconds, I get nervous," says Robin. "He's best on three-footers."