YUKON, Oklahoma - Some parents reached out to us, concerned a mixed martial arts instructor in Yukon was working with children even though he is a registered sex offender. So, we checked it out.

18 years ago, MMA fighter and instructor Eric Benton admits he made some mistakes. He served his time, but he says he's still paying for his crimes.

In the cage, Benton was unstoppable. Working with people with Parkinson's Disease, he shows patience and compassion. But when class is over and the gym goes quiet, his ghosts return.

"I'm still taking punishment" Benton said, fighting back tears, "still taking blows, you know?"

Back in December of 2000, when he was 28-years-old and living in Kansas, Benton met a girl. He says he thought she was older. Turns out, she was underage and he was convicted of indecent liberties with a child.

Back then, Benton says his life was all about boozing and brawling. He got out jail, put down the bottle, and put on the gloves, competing nationally and, with his wife, opening up a gym.

"He served his time," Tamara Benton said, "and he hasn't been in trouble in 20 years."

"I've made mistakes,” Benton added, “and I've done my time. (I) try to be the best man I can be."

But this keeps coming back to haunt him. He was placed on the sex offender registry for 10 years in Kansas but because he moved to Oklahoma and the law is worded differently here, Benton is on the registry for life. It's cost him customers and friends.

"They say that it's embarrassing to be our friend," Tamara said, "and it's a burden to stick up for us."

Benton added, "There's times when I want to quit, just give up, go back to the old lifestyle, but I look at how much it helps the people that come reaching out."

The Bentons say Benton never trains with kids. Children train in a different building.

The Bentons are trying to get Benton off the sex offender registry. But lawyers are expensive. And, even for a long-time fighter, this fight is exhausting.

"It's like the better I do, the harder they come at us," Benton said. "I'm not the man I was then. I can strongly say that people that know me, they know what kind of man I am."