I either use wooden dowels or the plastic dowels depending on the cake. I put one dowel in and mark it with an edible pen to just at the top layer of the frosting though I always cut it just a smidge shorter. I used to use scissors but it took forever. I now use a serrated knife, especially on the plastic dowels and it works perfectly. Once I have one cut, I use that one to measure out the others needed before sticking them back in the cake.
