I'd totally be up to magnet fish, but our bomb disposal department finds enough explosives from ww2 as is. Though I could use a pair of rusty bolt cutters used in some crime, as shown on the Wikipedia article ...
Magnet fishing, also called magnetic fishing, is searching in outdoor waters for ferromagnetic objects available to pull with a strong neodymium magnet.[1] Recovered items may be dangerous, such as firearms, ammunition, and bombs.
I'm not getting the 'better' part. You're much more stationary and whatever you pull up will be coated with muck and slime and, as what I pasted said, it might also seriously hurt or even kill you.
I'd say finding a bomb on a beach that no one has discovered yet is less likely than finding one in a river.