I have a stack of 3 stuck to the blade of my pick. They move around a little bit but never fall off. I do need to keep an eye on them, especially if a target in the hole "disappears". Often it is a little piece of iron stuck the the magnets.
They/at least mine are fragile so will shatter if you hit a rock with them.[/QUOTE
Mine are not on the tip of the pick. ;-) The magnets have been on the blade for over 5 years without any breaking. Small annoying iron (like shoe nails and staples) seems to magically jump out of the hole onto them. I never see it happen. Larger iron (spikes, metal plates, horse shoes, etc) are pulled by me by hand. FYI - I got the magnets from a local store called Lee Valley.