Whoever coined the adage “what goes up must come down” never looked into real estate, especially on Bainbridge.

Home and land prices seem to know just one direction: skyward. As such, real property may well make a better investment for retirement than the mercurial stock market – so argues island writer and commentator Tom Kelly.

But the real secret, he says, is the ease with which you can put a second home into your portfolio, use it as a getaway, then “trade up” for other properties as your goals change.

“For the first time ever, real estate has become portable, and not this stationary thing you can’t do anything with,” says Kelly, co-author of “How a Second Home Can Be Your Best Investment” (McGraw Hill, $16.95). Co-authored with John Tuccillo – a Georgetown PhD. and former chief economist for the National Association of Realtors – the book is written in a conversational style, aimed at “the average consumer” who may not believe they have the means to purchase a second home as an investment.

Says Kelly: they do. Investors can begin with the humble “Interim Property,” a starter that pays for itself through rental income. The equity can be parlayed into purchase of a “Cocoon Home,” a vacation dwelling the family rents out most of the year but uses themselves for family vacations. At the end of the rainbow is the “Ultimate Home,” the second residence in the perfect location that you wouldn’t dream of selling – perfect location, perfect size, perfect future.

Underpinning the strategy is a 1997 change to federal tax law that shelters sellers, even through a succession of transactions.

“What’s cool is, you can take this investment and turn it into your retirement,” Kelly said.

While the publisher’s press photos show Kelly in a suit and tie, he is probably more familiar to the locals in a Bainbridge lacrosse sweatshirt, on the sidelines or in the stands at prep sporting events.

He moved to Seattle from Southern California in 1975 to take a sports writing job with the Seattle Times, roughly coincident with the construction of the Kingdome and the return of big-time athletics to Seattle. That’s not to say his debut in the new market was auspicious.

“They needed bodies, and I was one of them,” he said. “One week I’m covering USC and UCLA at the Coliseum. The next week, I’m covering Foss and Federal Way.”

He worked the Times sports desk until one of the staff’s real estate writers went on leave, and Kelly – who earned his real estate license in 1976, after taking classes on his own initiative – was asked to fill in. That began a long stint covering the residential market as editor and columnist.

A decade ago, he was approached by KIRO radio to begin a real estate talk show; his syndicated program is now heard on 450 stations nationwide.

Kelly, his wife Jodi and their four children moved to the island in 1989 – paying their way onto the island, he says, by fixing up rental properties.

And if there’s such a thing as a sure-fire investment, Western Washington and its water-centric quality of life are it.

“People underappreciate what we have here,” Kelly says of the Puget Sound’s natural environment. “You can’t afford it in Southern California, and you can’t afford it in New England. It’s not possible in Middle America. And you don’t want to live in the Southeast.

“If you can’t see it, you can drive to it in a hurry – there are lots of options, and that’s the secret sauce.”