Mr Gersbach has never been charged over the alleged abuse.
His daughter said she was repeatedly sexually assaulted by him at the family's various Sydney homes and once on a bushwalk in the Royal National Park.
She also said that from when she was aged four to 11 her father made her bend across his bed and regularly hit her across her bare buttocks with a belt.
But Mr Gersbach testified to having disciplined his daughter, possibly five or six times, by hitting her on her clothed buttocks with his belt as she stood in front of him.
"They were firm strokes, to hurt a little bit, otherwise what's the point?" he said.
His daughter had been a happy little girl and a very good athlete, but later was bullied at school, developed an eating disorder and used heavy drugs, he said.
"I tried to be the best father I could be."
He said he spent thousands of dollars on her traffic fines, phone bills and on psychics whom she asked about the likelihood of her getting back with her boyfriend after a devastating break-up.
"All these lies told about me and false allegations have had a terribly negative impact on my business and all aspects of my life," he said.
"I have never sexually assaulted my daughter ever."
The hearing is continuing before Justice Peter Garling.
