Trying to keep a pricey collection of koi alive and well in your water garden with the likes of birds, turtles, raccoons, possums and house cats around is tough. But there are ways to protect water gardens and the colorful creatures swimming within.

Ed Beaulieu, an environmental scientist turned pond builder in Batavia, Ill., says ponds can be designed in such a way that foragers will avoid them.

To combat great blue herons, for example, he recommends installing a battery-powered sprinkler with a built-in motion detector and a range of 30 feet.

“Hook it up to a water hose,” he says. “Anything that breaks that electronic barrier gets soaked with a blast of water.”

A good decoy also works, he says. If your pond is big enough, you might consider building an island for resting or nesting birds. House cats, foxes and many of your garden variety meat-eaters aren’t all that fond of swimming.

Floating plants, like water lilies, provide fish and amphibians with cover from overhead predators, like perching kingfishers. They also create shady pockets in your pond, cooling the water in summer.