The Gorilla Safety Grill can be made to fit under the lid of any sized manhole cover and locked in place preventing people, animals and rubbish being washed into drains.
He said anyone could fit and secure one of his grills in less than five minutes.
They are made of galvanised or stainless steel for durability.
"Most drains are not big enough to cope with the volume of water after a heavy downpour.
"The secret is the steel mesh that can be locked in place under the cast iron manhole cover. If the cover blows off, the grill stops people falling into it."
He said they were not made for use on roads and were better suited to parks where children and animals could be playing.
In the past two years the 85-year-old, who says he won't be retiring any time soon, has produced more than 4000 grills for councils in Auckland, Whakatane, Tauranga and Rotorua. "It's a real Rotorua product too, all the production work has been done in Rotorua by Scorpro [Engineering and Development] and Patchell Stainless."
