Our picture shows Daniel Livingstone and Lachlan Judd of Wild Rivers pioneering prickly pear abseiling, the latest fitness craze to hit what remains one of the ACT's most spectacular natural features.

The challenge is to abseil down the rock face while attacking the extensive outcrops of prickly pear that attempt to impede your progress with a knapsack and a trigger gun.

Apparently, though I must confess to not being entirely across the rules, if you end up snagging your privates or with a cactus up your clacker you will be voted off the island … and that might be the least of your problems.

Seriously though, despite the best efforts of the justly celebrated Cactoblastis cactorum - the gallant little moth that was brought in from South America in 1935 to control the introduced weed - prickly pear remains a serious problem in this country.

Steve Taylor, the senior weed management officer with ACT Parks and Conservation, said Opuntia stricta (the proper name for prickly pear apparently) is a real worry along the gorge.

It is certainly not compatible with the natural fauna of gum trees, wattles, black cyprus pines, ferns and mosses and lichens that make this such an attractive spot even though it is just 25 minutes drive from Civic.

Given the ACT government has gone to the trouble of developing a lovely recreation area that includes dunnies (for all sexes), wood-fired barbecues and even playground equipment, it makes sense to go the extra mile to eradicate the spiky menace from the New World.

This is easier said than done when, in addition to populating the level ground at the bottom and the top of the gorge, the pear colonises the near vertical banks as well. That is where Mr Livingstone and Mr Judd come in.

Armed with 15 litre knapsacks of herbicide, really thick gloves and a raft of other safety kit including the mandatory hi-vis fashion garments all the go in outdoor work nowadays, they start at the top and then abseil down the rock face.

Tuesday was the last day of spraying in the vicinity.

''The strategy is already proving beneficial in weed management activities in other parts of Australia and it is allowing us to manage an infestation that would otherwise be almost inaccessible,'' Mr Taylor said.

''Because of the close proximity to the Molonglo River, eradication of the weed is vital as the area is home to endangered ecological communities and threatened species.

''The ACT government works diligently to control and remove invasive weed species from conservation areas to protect biodiversity.''

Prickly pear was introduced to Australia in the 19th century for two purposes; to be used to create extreme climate hedgerows and to create a cochineal dye industry.

It now ranks behind only the rabbit and the white man as an object lesson in why you don't introduce a species into an existing ecosystem that you haven't taken the trouble to study and understand.

The black-and-white photograph reproduced here was taken in the 1930s by workers with the Queensland Department of Agriculture.

It shows a prickly pear forest with plants growing three times the height of a man.

On a happier note, we have received the following missive from a reader who reported how a nasty mishap resulted in a happy outcome:

''Yesterday (Tuesday) afternoon I was in tdavihe car park of a large hardware store when I accidentally knocked a large piece of skin from the back of my hand,'' Jennifer of Dean wrote. ''In no time a young man came to help and brought the first aid box from his car. He bandaged my hand so very well I asked if he was a nurse. He told me he is in the army. I feel our country is in good hands being defended by such fine young people. Thank you for your help.''