Rob Thomas and His Wife Team Up With “MUTTS” for New Guard Dog Book: 'It Really Spoke to Us’ (Exclusive)

"We couldn't have been happier," the Matchbox Twenty singer says of being asked to write the introduction with Marisol Thomas

It's the 30th anniversary of MUTTS and a new book's on the way to warm your heart.

Matchbox Twenty singer Rob Thomas and his wife Marisol Thomas teamed up with cartoonist Patrick McDonnell for the long-awaited story of the inspiring character Guard Dog timed in celebration of the beloved comic's milestone.

Breaking the Chain: The Guard Dog Story chronicles the tale of a chained dog longing for freedom. His character debuted in the MUTTS comic strip in 1995 and now, three decades later, the book culminates with his unchaining and adoption.

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"There's such a beautiful simplicity to all of the Mutt's comics," Thomas tells PEOPLE exclusively. "But at the bottom of everything, it's a very, very deep and important message that he is trying to tell through these characters that fall in love with, but they're teaching you something as you go along."

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As longtime animal rights advocates and co-founders of the Sidewalk Angels Foundation, Thomas and Marisol were drawn to the MUTTS strip since the beginning — which is why McDonnell's offer to be involved was a no-brainer.

"When he first started to just acknowledge my wife and the work that she was doing with Sidewalk Angels, it really meant a lot to her," Thomas says of McDonnell. "The fact that MUTTS reached out ... We couldn't have been happier."

Read on for an inside look at Breaking the Chain: The Guard Dog Story!

The origins of Guard Dog

Guard Dog (now known as "Sparky") was first introduced in the MUTTS comic strip in 1995. Since his debut, the pup has become one of the most beloved characters in the strip.

Nearly three decades later, McDonnell says now was the right time to release a comprehensive book that encompasses Guard Dog's past and present. "I've been promising it for way too many years," he says.

Sparky was originally intended to be a "villain character" when they first came into the strip about a year after Earl and Mooch were introduced.

"I started drawing in my sketchbook what I thought was the typical nasty dog with big teeth protruding and I put a spike collar on them to look tough," McDonnell says. "Then I put a chain on that spike collar to make them look tougher."

But after doing so, the creator realized, "Oh, this isn't a villain. This is a tragic character, thinking about all the poor dogs who are chained in their backyards ... So that's how Guard Dog started."

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The thought process behind freeing Guard Dog

Readers of the popular comic strip often questioned whether Guard Dog/Sparky would ever be saved and have his chain removed.

"I’ve followed Sparky’s story for years, waiting for the day he would be freed and find his forever home," Marisol said, in a statement shared with PEOPLE. Though it took many years for fans to get what they wished for, the decision to do so was always in McDonnell's mind.

"I always knew someday I'd free him," the creator tells PEOPLE. "I'm friendly with a lot of animal organizations and groups and they all encouraged me to keep him on the chain because they thought he had a mission to raise awareness about the sad plight of tethered dogs."

The decision to finally free the character was "in part due" to his interaction with the Dalai Lama. "I got to visit him in India," McDonnell explains. "I was just in a different place in a different mood and I thought it was time to free Guard Dog."

Guard Dog's rescue story

Breaking the Chain: The Guard Dog Story chronicles the character's rescue from beginning to end.

"There's a little girl, Doozy, who befriends him and actually climbs over the fence to feed him and bring him blankets. It's the story of her helping Guard Dog go free," McDonnell explains.

"It's a really comprehensive book," he adds. "It starts with about 30 pages of the history of Guard Dog and his biography ... there's also the best of the Guard Dog strips, older strips that show what his life was like before the freedom story."

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Rob Thomas and his wife Marisol's love for MUTTS

As MUTTS celebrates its 30th anniversary this year, Thomas says he and his wife Marisol have been fans of the comic strip since the beginning.

"When I say a fan, I mean every day my mother-in-law and my wife send each other the strip of the day," the musician tells PEOPLE of how deep his love for the comic goes. "Every day she wakes up and there's a message on the phone."

Mooch the cat has a memorable way of talking, in particular, saying “Yesh!” instead of "Yes." Thomas says his wife "constantly" sends him pictures of the character in conversation with the funny word.

Rob Thomas and his wife Marisol's Guard Dog contribution

As animal rights advocates and longtime fans of MUTTS, Thomas and Marisol's involvement was a no-brainer to McDonnell.

"Marisol was a Guard Dog fan and one of the readers who really was hoping someday he would go free, although she totally understood his mission to raise awareness," he recalls. "I asked if they would be so generous to maybe write the introduction — and they both agreed."

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Rob Thomas and his wife Marisol's own animal rescue journey

Thomas and Marisol connected with the story of Guard Dog because of their own journey with animal rescue. It "specifically spoke to her," the singer says of his wife.

"Our first rescue, years and years ago, was a dog named Tyler, who was basically the same story. He was a chain dog that lived in West Virginia and was horribly abused," Thomas explains. "He was our first child really."

"Those are little characters that are a part of our life," Thomas continues. "I think anybody who's ever really let an animal be a part of their life and really be a part of their family just completely connects with Patrick's message."

The Guard Dog Story and Sidewalk Angles Foundation

Thomas and Marisol co-founded the Sidewalk Angels Foundation in 2003, a non-profit organization that strives to be the top supporter and sponsor of no-kill animal shelters and animal rescues, reflecting the couple's passion for the rights and fair treatment of those with no voice.

"We could actually be the impetus for change," Thomas says of their foundation. "We started really small with one organization at a time ... and now it's moved into giant, massive rescue operations all over the world."

Custom Guard Dog Merch with the MUTTS Living the Dream Collection

A portion of the proceeds for Breaking the Chain will be donated to the Sidewalk Angels Foundation. McDonnell also designed Guard Dog merch in collaboration with the organization and in celebration of the comic strip's 30th anniversary. It's part of the Living the Dream Collection which is inspired by the story of Guard Dog and the transformative power of hope, love and compassion.

"How cool is that? This is a geek moment," Thomas says of the foundation's MUTTS t-shirt collab. "The wings on Sparky are the very specific Sidewalk Angels logo wings — and so to see Sparky with those wings, my wife cried real tears.

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