I think I first saw this anchor trolley kit
on a Facebook page. The inventor was sort of polling his audience to see if there was enough interest in it to pursue makings molds and manufacturing them.
What caught my eye was the ring release mechanism itself and how flat it allowed the trolley to mount along the side of a kayak neatly. Then, too, note the system uses some hardware clips to keep the lines tracking along the sides in place and not twanging around. Anyway, a nice system. Look here: Neat Anchor Trolley System
Another device, the Deeper Fish Finder
, I was not familiar with is a floating fish finder about the size of a small orange. In videos I have seen, it can be cast out then reeled back in, results viewed on a smart phone, or it can be hanged off the side of a kayak with a little flexible holding device. I saw one deployment where someone was using a remote control toy boat to pull it around to get a look. I'm not sure how well it does finding fish but it apparently reads the bottom very well and its depth. Here it is with the Flukemaster reviewing it: Deeper Fish Finder