He completed the half marathon in the Cigna Round the Bays in Wellington earlier this year with a time of 3 hours 37 minutes and is aiming to come under 3 hours 30 minutes for this one.
"I walk through the bush about twice a week and make up long distance walks in the weekends ... I measure it in hours ... last weekend's was four hours.
"I want my first ever full marathon to be in Rotorua because that's where I'm from so I will be back next year to complete the full one," Mr Tuki said.
He trained every second Sunday with the Achilles group and the rest of his training was in his own time.
Achilles International NZ is a worldwide organisation that helps athletes with disabilities to take part in mainstream running events alongside able bodied athletes.
It is one of the official charities in this year's Rotorua Marathon, and has a team of athletes running and walking in various distances, including Rotorua mayor Steve Chadwick who will be guiding an athlete in the 5.5km.
Glennys Kereopa, Rotorua Achilles regional co-ordinator, said there were eight Achilles members entered in different distances this year.
She said each Achilles competitor would have a guide with them and this year they had 12 volunteer guides.
Marathon details
The Lion Foundation Rotorua Marathon will be held on Saturday, April 30. For more information go to www.rotoruamarathon.co.nz.