A bond, in the form of a cash bond or a bank bond, would be easily accessible and available. Mr Cooney said a Letter of Undertaking was too uncertain for the regional council to accept in place of a bond, as the terms could be disputed by Rena's insurers The Swedish Club.
A bond of $6.2 million was sought as well as a Letter of Undertaking for $36 million in case the bow section needed to be removed.
Another issue raised was what would happen if future monitoring revealed negative effects on human health or the environment caused by contaminants left on the wreck.
Mr Cooney said the big question was whether there would be an attempt to address this, or if no responsibility would be taken if causation could not be proved.
There were two key contaminants remaining in and around the wreck, TBT (tributyltin) and an estimated 16 tonnes of copper clove.
Mr Cooney said if the resource consent to leave the wreck on Otaiti was not granted, it could not be assumed that the owners would walk away and leave the wreck on site.
"The panel should not consider this application as though it has a gun to its head."
He said the panel could not require the full removal of the ship during the hearing process, but if the resource consent was declined, he believed a consequence could be the removal of all or part of the wreck.
Mr Cooney said the community and tangata whenua had conflicting views on what should happen to the wreck and remaining debris.
Some opposed the consent application believing refusal would result in wreck removal, others supported the application believing removal was costly and would further damage the reef. The others wanted the bow pieces and as much debris as possible removed.
In his conclusion, Mr Cooney said the key issues came down to how the potential environmental effects from leaving the wreckage on the reef could be managed and how Maori cultural values could be adequately recognised and provided for.
Diver: Rena safety risk only small
The safety of the Rena wreck as a dive site was assessed by a man with more than 6000 dives under his belt.
Simon Mitchell has dived shipwrecks all around New Zealand and the world for the past 42 years and has been involved in the Rena case as an expert on the safety of diving in and around shipwrecks on behalf of the applicants.
Dr Mitchell came to yesterday's hearings four hours after his most recent dive of the Rena.
He advocated for the Rena to remain at the reef.
"In my opinion, the hazard represented by the residual wreckage is extremely small.
"Concerns raised about the safety of diving on the shallow wreckage are framed largely around compilation of an inventory of hypothetical hazards such as trauma on sharp edges, trauma from wave effects around hard projections, entanglement in cables and adverse events whilst trying to perform tasks like retrieving artefacts.
"Notably, however, there is a conspicuous lack of evidence which defines the level of risk these hazards truly represent."
Dr Mitchell said it was possible over time that a small number of divers would be injured around the wreck, and there could be fatal accidents.
"But extensive experience tells us the risk is very small and probably indistinguishable from the background risk of diving."
