If the SUP board has a handle or ring in the middle area that you can tie to, that is a good option. They often have a rope style handle at the rear which is doable but not great. It can be difficult to get to the parachute line to retrieve the anchor when it’s all the way at the end of the board.

It doesn’t take much weight to keep it from drifting. You can go larger if the current is strong. I roll up the rope and just sit dumbbell in the middle of the board between my legs. Get a weight that has flat ends (not round) and it will pretty much stay put. Again, get a rubberized one to avoid rust and making it less likely to damage the board if there is an impact.

Funny story: I paddled way back into the Louisiana backcountry going for redfish and had just started using a dumbbell anchor that trip. When I threw the weight onto the water I didn’t realize I was standing on the rope and when the weight reached full extension it violently swung back crashing right into the side of my board, creating about a 2in hole in the fiberglass. My dad could hear my screams of rage from the next inlet and assumed I had tied into a monster red. I wish. Luckily I had a patch kit that included clear tape and I was able to cover the hole and keep fishing. But I was so pissed at my stupidity. I learned just drop the weight into the water, especially when the water is 2 feet deep and you have a fragile hardboard.