bx hill brake

Any one with a bx knows how the brakes are marginal. I have some steep hills that are wooded and I'm trying to clear some of the trees out. When I pull up the hill, set the brake and get off to load the fel bucket, the bx is slowly, and sometimes more thatn slowly moveing down the hill. These are spikes I made that quickly attach to the side of the quick disconnect. When I lower the 3ph, the weight pushes the spikes into the ground. It has held at the steepest hill with the fel full of logs.