V snow plow

I made a V-shaped wooden snow plow and used it to clear some snow this last weekend. It worked great over areas that had some snow cleared previously and had less than 3-4 inches accumulation. It also worked great at making a first pass on uncleared areas (we have over 2 feet of accumulation now). When I went back to widen the path, I had a hard time keeping the right edge of the V up next to the snow bank. The V tended to dig into the bank for a couple feet, then rotate out of the bank, then dig in again, in a rocking motion. It’s hard to ride and not very effective. I see that some of you use long runners underneath the V plow, I suppose these are to keep the plow straight… Are these enough to keep it straight or should I try something else? Maybe I should add some more weight to the plow? Is pushing this much snow is too much for this type of plow design? Thanks for any thoughts,
-Andy