Cacti don’t make it easy to keep the weeds down, you need good 3-D vision and co-ordination to avoid the spikes. I find it’s best to pull out what I can and snip the rest. Anyhow the cacti have much more extensive roots than the parasitic weeds so the summer heat in Marseille sees off the weeds more effectively than I can.
Many of these cacti need potting-up and separating but it’s not a task for the faint-hearted; though none of this collection have poisonous or irritant spines - one has nasty hooks and another some vicious micro-barbs - but all the gloves I have tried have been penetrated, then it’s actually a worse “sting” than on the naked skin.