Making a tool holder: how do you attach HDD magnets to plywood?

UPDATE: my original idea pretty much failed miserably. I glued up a strip of steel that I cut from a desktop tower cover to the backside of the plywood piece and then attached a bunch of magnets to it. I was using magnets with brackets. If I'd removed the brackets I would be able to put more magnets on the strip. But the way I had it, it did not hold tools well. Looked pretty but didn't work. So I'll try the sheet of metal idea next.