The 29-year-old body modification artist runs a licensed tattoo facility as a day job, but on weekends, he joins other body suspension enthusiasts in a Springfield, Mo., backyard.
But one neighbor insists that Shields and his fellow body artists are traumatizing his children and has pledged to ban the practice so young onlookers don't have to hear the screams and see bodies drenched in blood.
Aaron King, whose North Main Avenue backyard overlooks the meetings, says that his children should not have to be unwittingly exposed to the practice.
He isn't opposed to others doing it -- he just thinks his two children should not have to witness it, especially his 9-year-old daughter.
"She saw blood dripping from a shoulder blade area and what she said looked like holes," King told ABC affiliate KSPR. "I don't know why their right to do this should extend to public open space and force me to keep my children inside."
The Springfield group, known as the Anti Gravity Relaxation Organization or AGRO, is one of four other clubs in other cities across the country.
AGRO has used two trees in a private yard to build a pulley system to hang practitioners upside down with hooks pierced through their knees. Others zoom across a zip line with hooks under the skin between their shoulder blades.
"There is pain involved," Shields told ABCNews.com. "But it's not as bad as you would typically think."
Judging by Facebook groups devoted to body suspension, Shields estimates at least 2,000 to 3,000 men and women get a thrill from body suspension.
But in Missouri, there are no city or state laws against the practice.
"Why people do it differs," said Shields, who co-founded the Springfield club. "For some it's the spiritual sense and a kind of enlightenment and others just think it's fun."
But King thinks otherwise and has contacted his city counselors and several state agencies with his complaint.
City council member, Nick Ibarra said he agrees with King and told the Springfield News-Leader that he has asked the city's legal department to draft an ordinance that addresses body suspension.
One child development expert said she stands firmly behind King.
"It's the equivalent of taking a kid to an R-rated movie because of the violence," said Dr. Ari Brown, an Austin, Texas, pediatrician and author of several books on child behavior. "But you don't have a choice when it's happening in your backyard."
Young children might experience nightmares or anxiety after witnessing body suspension, according to Brown.
"Kids have a little bit of trouble understanding this type of thing -- it's violent and painful and someone is going through something uncomfortable," she said. "The visual leaves a lasting image in their memory and I don't blame the parent for being disturbed."
But those who enjoy the suspension club say any ordinances should protect participants rather than observers.
"We always push for stricter regulations," said Shields, who heard about the complaints after police visited their club a week ago.
"We were caught by surprise," he said. "The police showed up at our last meeting and saw what we were doing and told us we weren't breaking any laws but we should be considerate of the neighbors. We were pretty well done for the day."
"Our plan is to definitely be considerate of him and not go there anymore," said Shields, who said the group is so "passionate" about suspension, they don't want to jeopardize the club.
Suspension Artists Say Safety Comes First
Shields, who has practiced body piercing for six years, said the group is safety conscious. "Skin is resilient, but we watch for any possible rips during the suspension. We have a number of people observing to see if it looks good."
The group also checks its pulley system to make sure lifting ropes don't break. "We have a lot of safety -- I am a licensed piercer -- and so do all the tech people in our group."
He knows there are risks. With lots of blood, piercing hooks and equipment must be sterile and participants wear gloves for protection to avoid "cross contamination" of blood, according to Shields.
Typically the hooks are no wider than a number two pencil, he said. Most are much smaller. "Some [people] stay forever and some like to go off the ground," he said.
Shields said the feeling of suspension by the body's own skin is indescribable.
"I have done it and I can't really put it in words," he said. "Everybody is a little different, but I can tell you that when I go up I shut everything off and enjoy the weightlessness…The pain subsides."
The group says they take every precaution. "There are inherent risks, but we take every single effort to make sure it's safe," said Shields.
"There is a real sense of accomplishment, just making myself know that I can pick my feet off the ground and my weight is supported by a hook. It's about letting go."
Asked if he would let his own son, now 17 months, try body suspension, Shields replied, "Only when he's 18."