I just spray/water regularly using weed killer. The products laughably "boast" or rather admit, they don't last even a year, but what can one do ? (And they seem to come in daft sachets these days which one can not use half of and keep the rest until next time.) Yeah, it is, well caustic so be careful, but you can use caustic soda.
Or there are tools if you want to dig all the weeds out individually.