The suppression of fluid force acting on a square prism near a plane wall was studied by attaching fences to the corners of the prism. The height of the fences was 10% of the square width and the Reynolds number considered was Re=$2.0{ imes}10^4$. The experimental parameters were the attachment location and number of fences, the gap ratio G/B (G/B=0.1~1.2) to the prism. The average drag coefficients were increased and the average lift coefficients decreased and increased with the gap ratios toward the plane wall. The drag of the prism was reduced by 7.6% on average with the gap ratios by attaching a normal fence at the upper rear comer and a horizontal fence at the lower rear corner of the prism. By conducting a visualization experiment, it was noticed that the vertical fence installed at the upper rear edge generated a clock-wise vortex past the fence and reduced the separation region.