John Entwisle has been weeding the bluffs in Redcliffs' Barnett Park to help regenerating bush.
The 79-year-old, a retired professional alpine guide, told Checkpoint it was crucial to anchor the ropes properly at the top of the cliffs.
"If we can't do that, we either drill if we find good rock, and put in a couple of bolts and use those for our anchor of the rope. If it's on grass, we're hammering waratahs and passing ropes through them," he said.
"Our first thing is to get a really good anchor and then we've got devices that are fail safe that we put on to abseil. If you let go, it will just lock."
Entwisle said he was currently looking for boneseed, which flowered during August and September.
"They're a distinct yellow flower but they're quite distinct from the other two yellow flowers which are broom and gorse, so we can find them."
If the weeds were not plucked out, they sent more boneseed into the bush and down the slopes of the park.
"We're trying to get the whole area of Barnett Park and around the park, we're trying to get that back into native bush."
He said he and his fellow weed-busters had nearly weeded across the main bluffs. However, the seeds could lay dormant in the soil for five to 10 years.
"We'll have to go back yearly. I don't know how many years I managed to go back, but we'll go back yearly and just get them rather small, which is really easy, you can just pull them out by hand."
The challenge kept him going back, he said.
"It's outdoors, it's helping a large group of people who are passionate about getting this area of the park back to a native vegetation, attracting more native birds and getting rid of a lot of the noxious weeds that are there.
"We know from Hinewai Park and what Hugh Wilson did there that once we get our plants above gorse and broom, they tend to die out."
Entwisle said it was a good social atmosphere on the cliffs - and luckily, he was not afraid of heights.
"I was alongside my friend abseiling yesterday and we talked and joked as we went down about 10 metres apart.
"I've been on ropes since I was 15, climbing and abseiling, so I'm fairly used to it by now."
Entwisle said he loved the technical challenge of getting to some of the weeds.
"It's quite awkward because cliffs are irregular, you're trying to get round the corner to get at the weeds or they're out to one side," he said.
"You've got to be very careful that you don't lose your footing because if you're swinging, you can hit things. On the way down you've got to either pull them out or have a pair of loppers that are very sharp, and that cut the small, medium-sized ones and the really big ones to saw through."
