Stopping board sag?

[LeapFrog]

Could you cut strips of copper clad board, stand it up on end notch out some for clearance and solder it to the ground on the foil side in multiple locations?
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I might use this idea for a botched "amplifier chassis" build thank you.
Robb that document talks about "rough handling" as the cause; but in the pdf they say to use "rubber foam" anyways like Captain Kilowatt suggested, thank you gentlemen.
With all these ideas/suggestions it shouldn't be too hard to stop the sag from progressing.