Good idea!
I just use a heavy weight at the end, with a "longer than the water is deep" rope and a decoy at the end. I keep the boat in gear to pull the net tight, and drop the net to the bottom, pulling on the rope/weight to keep the net tight.
What size is the basket (H, W, and length) on your Fyke Net, and what is the mesh size? What size is the lead?