I have one cant block that is cut to the shape of the barre, 1/2 octagon, and has a screw through the bottom and into the bottom flat of the barrel. The octagon shape keeps it from rotating. I have another that is a block of wood that has an octagon hole through it and is then cut in half. The top of the octagon hole is flush with the top of the lock. A trough bolt fastens the two halves onto the barrel. I can send pics of both if you want to see what I'm talking about.
Mark