University staff have told Mr Schapel they questioned the Shark Shields' efficacy and believed there might be long-term health risks from using them. As a result, the devices were not compulsory.
Rod Hartley, director of Sea Change Technology, which manufactures the Shark Shields, yesterday took the stand to defend his product.
"There is no doubt whatsoever that it does not attract sharks," he said.
He told Mr Schapel he believed a disgruntled surfer had started the rumour.
"Nobody wearing a Shark Shield has ever been attacked by a shark," he added.
Mr Hartley said the failed South African test on the surf unit - which has been held back from release into the marketplace - was due to a problem with the electrode's configuration. The device was now packaged with a large disclaimer warning it would only repel sharks when the surfer was still in the water waiting for a wave.
"The surf product only can be guaranteed to work when it's stationary, not when it's surfing in the wave or paddling," Mr Hartley said.
CSIRO shark expert Barry Bruce has told the inquest the shark that killed Stehbens was in "full predatory strike" mode and would have been nearly impossible to deter. His body was never recovered.
Mr Schapel will publish his findings at a later date.
