I have a long 24" (?) x 5" cutting ruler with a lip on the perpendicular bottom 5" edge that hooks on the cutting mat. With my left hand on the ruler walking down as I cut, I slightly push forward so as to keep pressure on the lip, and then cut with my rotary cutter in my right hand, This lip acts like a third hand, and if you keep the rotary cutter vertical, and cut straight down , slippage is minimal if at all.