Hands down the best fishing magnet you can get.
https://www.edmundoptics.com/lab-production/magnets/edmunds-heavy-duty-magnet/I've had one for almost thirty years and it's still very strong. When it was new I put it on a thick plate of bare iron. I had to use a crowbar to get it off. If you get this use good nylon rope, a sturdy knot, and be prepared to pull hard enough to capsize a canoe if it gets a grip on something heavy.
