I have some height-adjustment nuts screwed onto vertical threads to support my print-bed for a 3D printer. They are domed nuts and the aluminium build-plate sits on top of the domes, three holes in the plate align with the domes to hold the plate in place.
How can I protect these nuts from vibration loosening without using thread-locker or similar, so that they remain adjustable?

The double nutting application referred to in the answer above is similar, but the typical application more like a precursor to today's nylon lock nuts or locking washers.
– DLS3141 Jul 22 '15 at 16:19