Weed control under gravel

I laid some gravel around my ac unit to create some spacing between the grass and the unit to make cutting the yard easier and to keep grass clippings away from the unit. It's on the side of the house where no one goes, so I really didn't do it for aesthetics though I did brick outline it and it looked nice enough when I first completed it.

I thought the rocks and some weed spray would be enough to keep the weeds under control but they are still being problematic. First of all, I have torpedo grass and it is the spawn of Satan. I have come to terms with the fact that I will not be getting rid of it. I thought the rock garden would keep it down unlike my mulch garden in the front, but that has not been the case. It's not the biggest deal ever because, again, it's just an ac on the side of the house, but I'm still considering what my options are because I don't like weed eating right next to the ac unit or in the rock garden and pulling them is a bitch and generally just results in them breaking off at the rock line and coming right back.

What are my best options for making life easier on myself? I thought about pulling the rocks out and just laying plastic down underneath the rocks since I don't have any plants in this area at all but then I figured that might cause some drainage problems. I have heard landscape fabric is pretty much useless against torpedo grass but maybe it would be worth it to keep the other weeds down and make targeting the torpedo grass easier? Any other method that might help with this?