[Uptown Girl]

I keep a generous layer of pine straw around the front landscape and most of the plants I treat this way are located there.
I find the pine straw is very easy to literally roll back. (using a claw type hand tool and my hands) I then have free access to lay down the Black Kow and then roll the straw into place again.

I know that a lot of folks don't care much for pine straw, but I find that a 4" deep layer right over the dirt has eliminated almost all weeds for me. I find maybe one or two baby weeds weekly and just pull them by hand.
I bought a large container of Preen a year ago.... but only seem to need it occasionally along our CYV fence, as the neighbors grass creeps under that.
I pull back the straw, remove the zoysia creepers, sprinkle a line of Preen and reposition the straw.
Takes about 5 minutes quarterly.

The plantings in our back have rock as a ground cover, so I do not use the Black Kow there. (do use the Osmocote, sprinkled on top of the rock) Again, our rock is pretty deep, and I think that helps. We have had it since early summer and I have hand picked three weeds so far, but I did see the landscaper take extra care to prep the ground before the weed barrier was laid beneath the rock.

I imagine that over time, as airborne dirt accumulates between the rocks, there will be places where a weed seed can take hold. I may regret the rock some day. But as time goes by, the plants grow larger, so less rock or pine straw will be visible as our stuff matures.

I have seen homes where weeds are runaway in the rock beds. I have watched landscapers lay weed cloth over existing weed beds and rock over that. Not so good.

Short of re-doing the underlayment, I guess chemical treatment would be most practical, being careful of the plants you do NOT want to kill. You still have to pluck the weeds after they turn ugly and dead, however.... for me they're easier to pluck when they are green. That is, with a good pair of garden gloves to protect your hands from things like rocks and critters.
Happy Gardening!