Harry Hamlin on the Secret to 25 Years of Happiness with Lisa Rinna: 'We're Diametrically Opposite!'

"I like going up to the mountains, and her idea of camping is anything below the 10th floor of the Four Seasons," Harry Hamlin jokes to PEOPLE about his wife of nearly 25 years, Lisa Rinna

Harry Hamlin and Lisa Rinna know a little something when it comes to love.

In this week's issue of PEOPLE, the couple opens up about their nearly 25-year-old love story — and the secret to a successful, happy marriage.

"[The secret is] being diametrically opposite," says Hamlin, 70. "I like going up to the mountains, and her idea of camping is anything below the 10th floor of the Four Seasons."

Adds Rinna, 58: "We'll be married for 25 years in March, and I've worked hard. So I've picked out a very nice diamond."

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The playful banter comes easily to Hamlin and Rinna, who share two daughters Delilah Belle, 24, and Amelia Gray, 21, but the road to happiness had its early bumps.

"She played hard to get," says Hamlin — who will next be seen in the Lifetime miniseries Flowers in the Attic: The Origin — of his first attempts to court The Real Housewives of Beverly Hills star.

"The Rules (a trendy self-help guide to dating) had just come out and it was written by women, for women to teach them how to get a man," he recalls. "And in that book, one of the rules was, if you were called up by somebody and they asked you on a date, you had to say, 'No.' You had to wait at least a week or whatever. And I knew that she had read that book."

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The actor adds, "So I called her up and I said, 'Do you want to come to dinner at this Italian restaurant?' and she said, 'When?' I said, 'Well, how about in an hour?' And I hadn't talked to her in months. And, she showed up and broke all the rules."

"I'd just come from work [on The Days of Our Lives] and had no makeup on," recalls Rinna. "So I guess I wasn't playing that hard to get."

Over the years, the couple has learned that a successful marriage boils down to mutual respect and an unwavering willingness to listen.

"We've always heard each other," Hamlin says.

Adds Rinna: "And it doesn't hurt that he's so good-looking."