Best Weed Killer

What is the best weed killer? The slope in the pic is part of my yard, it's about 35 reaching to 40 degrees and is very unstable because of the bark.
I have mobility issues and every time I go up there I am worried I'll have a fall and seriously injure myself.
So I need something that will stop regrowth so I go up there as seldom as possible.
I've been using Brunnings Glyphosate from Woolies, I've tried 20, 30 & 40ml per litre of water, it kills the weeds but won't stop regrowth.
Recommendations? Ideally a concentrate I can mix, I have access to ABN if something good is not available over the counter.
Cheers
PS The pic is an old one, the weeds up there now are dying but they will just regrow
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You need a residual herbicide, glyphosate is designed to rapidly decompose once it hits soil.

Though I haven't used it I would expect that Bunnings Path Weeder would be the sort of product that you need and it is readily available.

Another alternative is to find a farm supply store and talk to them,

What Bohdan said although I think it is Brunnings brand available at Bunnings.
I have used it in the past and it does work.

Salt!!!!

Tried kilograms of salt (read many Kg's) on a small area, with very limited results. This surprised me as the rate was circa 1Kg/1.5m2.

ULP

On a serious note you need something like weedstop from weedforce. It about $75 to cover 1000sq and lasts about 12 months

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I tried salt and vinegar mixed 75grams of salt, 1 litre of vinegar and 10ml of dish washing liquid - that's a mix I found on several websites.
It did sod all for the weeds, about all it did was give me a craving for fish and chips.

Don’t use Salt, all it will do is poison the soil. Have you thought of planting ground covers?
If you want to try residuals go to your farm supply and ask about Simazine or Prolan. Problem is that most residuals require bare soil to be applied to and the mulch will lock up the herbicide.



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Probably in your situation - I think I would put down one or two layers of quality woven landscape fabric and blow ground up tire mulch over top of it. You may get the occasional surface weed - but nothing will be able to set good roots or really grow through it....

Thanks for all the information folks, much appreciated, I ended up going with the Brunnings Path Weeder.
If this was place I would definately go for weed matting (in fact if this was my place I'd dig that slope out and make the space usable) but my owner while excellent with repairs won't do anything beyond what's absolutely necessary and I'm not going to pay for it myself - I am running up my power/water bills every month pressure cleaning the paths because the owner won't get the roof cleaned and the paths are filthy after every rain.