If your stencil design is too close to the edge, could you tape on something to the edge of the stencil to give you more of a border. Maybe tape on a strip of wax paper or something? Then you wouldn't have to worry about your brown going outside of the stencil. As far as spacing the design, the ribbon, paper idea sounds good especially if your designs are different sizes. If you have design that you need evenly spaced I have used the Wilton cake dividing wheel with good results. It is a circle of clear flexible material with lines radiating out from the center. You center your cake on the wheel. If you want 6 designs going around the cake just put a little mark on the cake where each of the 6 are on the grid and it will be evenly spaced. It works with any cake size and I think will divide any number of times up to 12.