Glenn Bradley showed his Anti-Racking Device >> HERE << and as I now have two working vices, I thought I'd make one.
I made mine a little bit different......
I just figured this was even simpler, no sliding parts.
I used two different thicknesses of plywood, 10 mm and 4 mm, and a few of each, so I should be able to get just about any thickness needed.
Works great too!