The Far North District Council has seized the terrier-cross dog that allegedly attacked 95-year-old Jim Morgan on Monday, along with another that was not believed to have taken part in the attack.
The owner was not at home.
Meanwhile four animal management officers who went door-to-door in Harold Ave to check that dogs were registered and adequately secured found 16 in all, five of them, including the two that were impounded, not registered.
The dogs at the address identified by Mr Morgan had not previously been reported for aggressive behaviour.
The council's environmental services manager, Darren Edwards, said since the December 16 attack on Mr Morgan and his dog, animal management officers had stepped up door-to-door registration checks at homes along and around Harold Ave, resulting in dogs being impounded and notices to register issued.
Similar checks and patrols were being conducted regularly across the district.
"Our staff take their responsibility to enforce the Dog Control Act and the dog control bylaw very seriously," Mr Edwards said.
"Unfortunately, there are several areas in the Far North where there are persistent dog control problems. We have focused our enforcement efforts on these areas.
"We ask members of those communities to help us keep their streets safe by immediately telling us about aggressive and uncontrolled dogs. Where necessary, we also ask people to help us with prosecutions."