Another neighbour, who refused to be named, said it appeared he had accidentally driven forward off the cliff instead of going backwards.
"He never mows his lawns with someone else's tractor. He usually used a push mower. He knows what he was doing. He'd been farming all his life. It's just one of those things," he said.
"His dog hadn't left him all night. It was pining for him. Even when we took it away it was upset its owner was dead. They were obviously best mates."
The neighbour said he was well known by local residents and would be missed.
"He was always loud. You could always hear him coming. He was a really good neighbour, he would always help out," he said. "Everyone on the street - and we live on a long street, it's about 16km long - everyone would have known him. He did what he could to help."
Mr Keenan had never married and had no children but had a brother and sister-in-law who lived in the region.
Mr Dawson described his neighbour as a "bit of a unique character".
"He was a brilliant neighbour. He was a real rough diamond - very helpful, very supportive and an all-round good guy. He knew everyone in Tauranga," he said. "He was a character that had nine lives. When he was 7-years-old he had his last rites read to him. He lived through a number of other things."
He had been sick for much of his life and had spent many years in Tauranga Hospital as a child, Mr Dawson said.
Despite being a beneficiary and unable to work for most of his life he had still managed to work in the concrete industry and helped with the construction of the Kaimai Tunnel for a time. He was also a keen surfer and diver, he said.
A strong Catholic, he was also proud of making it to Rome despite his ailments, Mr Dawson said.
His family was well known in the area and Mr Dawson understood they were also related to the Kennedy family in America.
"You could write a book about him and it's all true."
About 15 people gathered at a neighbour's home on Omanawa Rd last night to remember Mr Keenan. "The community said we've got to have a bit of beer on poor old Dennis. He'd always been on his own and he'd had some pretty tough times," Mr Dawson said. "He was a great neighbour and a great friend."
Neighbour Simon Kendrick also described him as a loyal friend. "He was a rough diamond. Pretty respected around the neighbourhood. He had nine lives and this must have been the ninth."
Police said his death had been referred to the coroner.