This suggestion that I saw in one of my old beading magazines really worked for me. I tried it this weekend. I wish I could give credit where it is due but the magazine is now long gone, apologizes.
Cut holes in a piece of beading felt - I also tacked each end down with pins just to keep it from even think about slipping! Then fill each hole with your beads. I even mistakingly hit my beading board a few times and a dog paw appeared in the middle of it at one point, but everything stayed fairly well in place.