Like the idea of the hard drive magnets. I made a couple of handles for some I've got but they're the right shape to put next to side of grinder so will give it a try.
For a larger magnet try removing one from a microwave ( the magnetron that generates the microwaves has 2 powerful ring magnets) but take care not to fracture them or get any bits from the magnets in you as I believe some early ones may contain beryllium ( toxic) not certain of that though as it maybe just the insulator which you don't need or want.
The resulting magnets are about 3" across with a 1" hole in and come in handy for all sorts
You usually need Torx drivers to disassemble the hard drives, and some screws are hidden behind stickers and labels. For data destruction, it is important to separate and remove the individual platters from the stack. Put each separate platter in a plastic bag, and bend it a few times with pliers (not hands!!) to destroy the data. Wear eye protection!! Some laptop drive platters will shatter into tiny glass shards, which is why using tools through a plastic bag and wearing eye protection is essential.
Most hard drives have two neodymium magnets; a few rare drives have only one. They are flat and slightly curved, welded to a steel frame. Separate the magnet from the frame by bending the ends of the frame away from the magnet with pliers. Neodymium magnets are brittle and can shatter, so wear eye protection!! Prying with a screwdriver may result in breaking the magnet.
Be careful with the powerful magnets, which can easily pinch off skin when they come together. They are very very strong and can easily scratch surfaces, so they are not suitable for refrigerators. They are especially dangerous for children. Separate them by sliding them apart sideways.
They are useful for projects where they can't be seen, like behind a paper-thin strip of wood. They are useful for the shop. I use one to hold adjustment tools on my bandsaw, for example.
I hope this helps.