Gail Harper called the Comment News in distress after witnessing the incident while driving her son home on South West Highway.
She believed she saw the developer’s contractors driving kangaroos on to the road.
Cedar Woods WA State manager Stuart Duplock said the fault lay with the ‘irresponsible member of the public’.
‘Our contractors were attempting to allow the kangaroos back into the Stage 1 area while the dog was being captured,’ he said.
‘They did their best to capture the dog and allow the kangaroos safe passage back into the site.
‘The member of the public was spoken to but left the site quickly.’
Serpentine Jarrahdale Shire representatives on site at the time saw the incident.
Cedar Woods has now installed more fencing. The existing fence is part of its plan to migrate the large kangaroo population off the site, which will not support them once developed.
Cedar Woods engaged consultants to prepare the plan encouraging the kangaroos to move to nearby forest and regional park through corridors to the site’s east, furthermost from the highway.
Mr Duplock said the consultants, including an experienced zoologist, would monitor the situation.
‘The plan is based on minimising stress to the kangaroos,’ he said.
‘Alternate strategies would only be considered should the preferred migration strategy not be successful.’
The Department of Parks and Wildlife has approved the plan, which a departmental spokeswoman said she understood had so far had ‘some success’.
Asked whether culling would be a legal option if this did not continue, she said the developer must apply to DPaW for a licence to carry out a relocation ‘or other measures’.
Shire chief executive Richard Gorbunow said the Shire also supported the plan.