When work is done, the cost is shared between the council, the landowner and government.
In the 2012-13 year, SLUI did twice as much work on the ground as it had targeted.
Staff were thrilled with an AgResearch report that said the first 10,000ha of work would keep 0.44 million tonnes of sediment out of waterways. There are now 17,000ha of work completed, and Mr Cooper said the initiative could run for another 15 years.
"It showed us that we were on the right track - we've just got to keep at it."
In 2012-13 nearly 3500ha of forest was planted, with all the trees destined to be harvested.
Most were pines, which are cheap to plant and provide the best value for ratepayers and government. Species such as redwoods and cypress are planted if they are the only way to make the forestry economic.
Also during the year 1800ha were fenced off and retired from grazing, to revert to native bush. Mr Cooper said farmers could be reluctant to lose income from land, but often changed their minds when confronted by hillsides reverting to gorse and feeding few stock. The council helped with fencing costs.
"If it's on erosion-prone land we will put a good amount of money into the fencing of those blocks."
Another 453ha was retired from grazing during the year, to protect wetlands and the banks of rivers and streams.
Some farmers were opting for "managed retirement", where they stopped putting fertiliser on areas and grazed only with sheep. The result was land gradually reverting to forest.
One possible economic benefit from allowing scrub to grow into forest was carbon credits. Another was manuka honey.
"It's still in its infancy but there are people now offering reasonable money for that sort of thing."
As well as full tree cover options, 18,700 poplar poles were space-planted on eroding hillsides during the year.
The SLUI is not likely to be as productive in the next few years. The Government has stopped funding forestry with its Afforestation Grant Scheme, and changes it has made to the Emissions Trading Scheme have reduced the value of carbon credits.
The result of the double whammy is that only 1000ha of new forest planting is planned for the coming year, a big drop from 3500ha. It could be a while before planting increases too, because forestry needs forward planning.
"You just can't turn forestry on and off like that. It has 12 to 18-month lead times, to order seedlings from nurseries."
Horizons will now have to find other sources of forestry funding. In the meantime, Mr Cooper said it was trying to plant more poplar poles.