A Mosgiel man who believed he was sexually grooming a 14-year-old girl online has been sentenced to five months' home detention.

The schoolgirl was actually an undercover police officer, the Dunedin District Court heard this morning, and Evan Hedley Smith, 63, was finally arrested waiting for the teen by a playground in December following the three-month sting.

It came just six months after the defendant was acquitted at trial on two charges of rape and six of indecent assault.

A jury unanimously found him not guilty over allegations he had abused a similarly young girl over 18 months.

Today, Judge Michael Turner said Smith had shown "questionable" remorse for his behaviour, telling Probation he was not planning sexual contact with the girl and only wanted to see what she looked like.

He was added to the Child Sex Offender Register.

Despite his scrape with the justice system, Smith began communicating with who he thought was a teenage girl over Facebook in September 2018.

The undercover detective – part of the Online Child Exploitation Across New Zealand team - told him she was living with her mother in Wellington while her father lived in Dunedin.

She made her underage status clear but it did not deter Smith, who called her pet names hundreds of times over the course of their contact and described her as "beautiful".

By November, he professed his love for the teen.

When she claimed to have recently turned 14, he reassured her age was "only a number".

It would be good to have some company if she came to Dunedin, Smith later told her during their frequent communication online.

The police officer operating the account told Smith she was coming south to visit her father and the defendant soon set about persuading her they should meet.

He continued to declare his love for the girl and said he was jealous when she told him she had been speaking to boys.

Smith asked her if she was a virgin and when she admitted she was, he reassured her with stories of his own first sexual experience.

A date and location was set for their first rendezvous.

What should the girl wear?

Nothing, Smith joked.

The man parked up by a Dunedin playground at the agreed time where he was arrested by police.

Smith later tried to convince police he was only going to meet the teen to tell her their relationship was inappropriate.

Judge Turner described that as "nonsense".

The Crown invited the court to confiscate Smith's vehicle since it had been used in the commission of the offence, however defence counsel Cate Andersen said that would result in severe hardship to her client because he still owed more than $6500 to a finance company for the car.

The judge declined to issue a confiscation order but banned the defendant from driving for six months.