EXCLUSIVE: Heather and Terry Dubrow Reveal the Surprising Secret to Their 17-Year Marriage

'The Real Housewives of Orange County' stars invited ET behind the scenes of the cover shoot for their new book.

Heather and Terry Dubrow are ready to introduce you to Dr. and Mrs. Guinea Pig.

The couple is set to release their first book, Dr. and Mrs. Guinea Pig Present the Only Guide You’ll Need to the Best Anti-Aging Treatments, in September, and only ET was behind the scenes as the couple shot the cover.

“We’ve done every kind of non-invasive plastic surgery rejuvenation you can possibly try,” Terry tells ET. “Basically, we’re giving everyone who’s interested in looking their best and feeling their best all the best beauty secrets you can find anywhere on the planet, that work. And we’re telling you the ones that are very popular that actually don’t work.”

“So, it is real or is it snake oil?” Heather adds. “We are Dr. and Mrs. Guinea Pig, and that’s what our book’s about.”

WATCH: Heather Dubrow Opens Up About Losing $2 Million in Business ‘Scam’

The couple says they’ve tested “every lotion, every potion, every treatment, every surgical procedure” under the sun -- including leech therapy, as documented on The Real Housewives of Orange County.

“That’s just one of the many lengths that we went to, to make sure that we were bringing consumers, you know, every single treatment from a scientific point of view, and from a consumer point of view,” Heather says.

The book is just the latest joint project for the couple, who will celebrate their 17th wedding anniversary this year. Along with the book, they have their anti-aging product line, Consult Beaute, and co-star on the aftershow for Terry’s plastic surgery series, Botched: Post Op.

The Dubrows say working together is actually the best thing for their marriage.

“We don’t work together full-time, so when we get to do something like writing our book together … that’s a labor of love for us,” Heather explains. “It’s really fun that we get to be creative and passionate about something together.”

“I think that’s the secret of a relationship where two people are very busy,” Terry says. “Find a way to work together if you can, even if it’s just a hobby -- something… cooking, or exercising, or working in many projects like we do -- this will keep you happy, this will keep you together, and this will keep you excited and interested.”

WATCH: Heather Dubrow’s Advice for Real Housewives Co-Star Vicki Gunvalson -- Hibernate!

Of course, working together isn’t the couple’s only tip for a healthy and happy relationship.

“We make a concerted effort to be together,” Heather says. “We make sure that we have date nights. We make sure we schedule sex … It’s very important to have to stay connected. Whether it’s taking a walk together, you know, going to the gym together, going out to dinner together, you have to have alone time. Even if the babies are napping, you must make it happen.”

“One thing I’ve discovered recently is FaceTime!” Terry reveals. “I love to FaceTime Heather in the middle of the day.”

“This is annoying,” Heather laments. “It’s so sweet, but sometimes we’re not camera ready.”

“But you know, if I have five surgical cases, which I do tomorrow, and I won’t be able to see her necessarily ‘til the wee hours of the evening, I can spend some serious time with her in, sort of, almost in person,” Terry says.

WATCH: Housewives Happy Hour With Heather Dubrow

Oh, the couple has one more, uh, unique suggestion.

“My biggest tip for a very healthy relationship is separate bathrooms,” Heather says.

“Which we don’t have right now,” Terry confesses. “But very soon in our new house.”

“We’re muddling through,” Heather jokes.

Speaking of that new house, check out ET’s exclusive tour of the couple’s under-construction Orange County mansion in the video below.