Trimming miters used to drive me crazy, because I couldn’t hold the piece I was trimming securely enough against the miter gauge. The piece would always slide away from the blade during the cut. I solved the problem by covering the miter gauge face with 120-grit PSA (pressure sensitive adhesive backed) sandpaper. One 5-in. disc will cover most gauges. I clean the face with denatured alcohol, to assure good adhesion. Then I simply cut the disc to fit the face and press on the pieces.