Hey Tony,
Back in the day on my fishing kayak, I rigged up a rubber coated 5# dumbbell on about 20' of line which was more than adequate on my rivers, (think Stillwater, Great Miami as far as size/depth). I set the anchor line up with a quick release in case it got hung up. On the end of the anchor line in the boat, I had a piece of pool noodle as a float so if I had to release it, I could paddle back up and retrieve it. In slow moving water, the anchor would hold me....in faster moving water, it would slow me down enough to be able to fish.
Mike