"My daughter and son-in-law kept trying to scare him away, but he just kept coming back," Ms Morris said.
Della Kaur, owner of Burwood Manor Motel, where they were staying, called the district council to get the dog picked up.
She was told they would get back to her but didn't.
In the morning, Ms Morris and her family were leaving for Auckland and didn't want to leave the dog alone, so gave Mrs Kaur contact details and took Duke with them.
"I'm an animal lover," Ms Morris said.
"There was no way I was going to leave him for somebody to pick up, because they use them for fighting and things."
Mrs Kaur called Mrs Lacy after seeing Duke's picture in the paper on Saturday.
"The motel owner said, 'There was someone staying here that has your dog. She's left contact details but she's from Auckland and she's taken your dog'," Mrs Lacy said.
"I was just so happy that he was alive. I was a bit worried I was going to find a body on the side of the road."
Mrs Lacy had visited the pound every day since Duke went missing, as well as driving the streets looking for him.
Ms Morris said she was "rapt" when they found the owner.
She knew keeping Duke was not an option because she had her own dog - a male American bulldog cross.
Mrs Lacy said her other English bull terrier, Lola, who had been with Duke since they were puppies, had been "moping" since he went missing.
Conveniently, Mrs Lacy had friends who were in Auckland at the weekend and they were able to take Duke back to Wanganui with them on Monday.
Mrs Lacy asked why council staff had not picked up Duke when he was at the motel and was told the call was lodged at 8.20pm on Saturday and was low priority. Higher priorities included the likes of vicious dogs and loose stock.
She said she was not pleased with the answer.