Hamilton and Reece dish on the challenges and joys of family life in the new documentary, Take Every Wave: The Life Of Laird Hamilton

Legendary big-wave rider Laird Hamilton and pro volleyball champion Gabrielle Reece are revealing the secret to making their nearly 20-year marriage work.

“I say it’s called a relation ‘ship,’ ” Hamilton, 53, tells PEOPLE in this week’s issue, on newsstands Friday. “We are in a boat, we have to work together. Sometimes it’s stormy, sometimes it’s calm, but you have to put the effort in and you have to want to.”

Hamilton jokingly adds, “I just agree with everything that she says, and then it works fantastic.”

The athletically gifted couple wed in November 1997 and share daughters Reece, 14 and Brody Jo, 9 (Hamilton has a daughter Izabella, 22, from a previous marriage). Keeping their marriage alive hasn’t always been easy, though, as they considered divorce during one rough patch before being able to work things out.

In her 2013 book My Foot Is Too Big for the Glass Slipper, Reece, 47, made headlines when she advocated for women being “submissive” in a relationship, but now she says that the secret to their marriage’s longevity is “understanding that if you have someone you really love and respect, show them you admire them, appreciate them and even desire them on a regular basis.”

“We always joke, ‘You go make yourself happy, I’ll go make myself happy and then we can come together and work from there,'” she continues. “Not, ‘It’s your job to make me happy and my job to make you happy,’ because that’s not realistic.”

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Credit: Jeff Lipsky

As to what happiness means to Reece, it’s facing new challenges. “I so enjoy being a mother and a wife, but I need to have my own outlet as a person,” she says. “I [find ways to] challenge and express myself other than being someone else’s something.”

For Hamilton, it’s a bit simpler. “The way I find my happiness is I ride a wave, ride it really far, ride it really big and ride it really fast,” he says.

A new documentary, Take Every Wave: The Life of Laird Hamilton, directed by Rory Kennedy, takes a dive into Hamilton’s difficult childhood growing up in Hawaii, awe-inspiring career and the challenges and joys of the couple’s family life.

“I really didn’t know what being scared was until I had kids,” Hamilton says. “If they’re hurt, you can’t take away their pain, and that makes you feel vulnerable.”

Reece calls being a parent “the most rich experience and the most difficult,” and that “sometimes you hit it right and sometimes you miss.”

For more on Laird Hamilton and Gabby Reece, pick up the latest issue of PEOPLE, on newsstands Friday.