The City Guardians were established by the council in 2011 after more than 300 businesses signed a petition asking the council to part-fund the group, saying they were sick of anti-social behaviour, crime and intimidation on the city's streets.
Mr Mumby has been employed as a guardian for three years and was previously employed in forestry security.
"I wanted to make a difference," he said. "I enjoy working with the team and our interactions with the public are fantastic. There are a lot of good people in Rotorua."
He said they use their discretion to deal with incidents and call 111 if it is something beyond their means.
"We do get a lot of angry people on the street but it's a matter of talking to them and trying to calm them down. We're in the city for everyone. It's a team effort."
The other City Guardians are Gina Marsh, Helen Coombes and Jenna Samuel.