To prevent a belt sander from tilting near the edge of a workpiece and rounding over the corner, place another board that's the same thickness up against the workpiece. This way, the sander rides across the edge and on to the abutting board instead of rounding it over.
If vibration causes nuts to constantly work loose, first add a lock washer, if it doesn’t have one. Or, if there is room on the bolt, use two nuts, tightened toward each other so they lock solidly. You can also try wrapping monofilament fishing line under the nut before tightening it on the bolt. Another possibility is to try wrapping the threads first with the teflon tape that is used in plumbing.