Toph said..
I have 60m of 10mm chain and another 50-60m of nylon. Even with that I only slept best after purchasing a Rocna anchor (not soundly, but better).
After 185 consecutive nights (not true there were some marina stays) on the pick it only let me down once and that was with multiple attempts to set it. Once set even with 45kt winds over 4 straight days it held solid.
Just out of interest where did you have trouble setting the anchor and what was the bottom?