do you have to put a trimmed cake board under each tier of a tiered cake?
ok, I tried a tiered cake for the 1st time and I had trouble with the smallest cake sliding around off the board while I was trying to frost the sides, not sure how to get it steady enough to frost it evenly
Try putting a dab of icing on the cakeboard - should help with it sliding while icing 
Always (in my opinion) put your cake layers on cake boards when stacking. You can sharpen the end of the dowel rod a bit to help putting it all the way through the layers with a XAteco knife.
Just practice and find out what works for you best 
with the wooden dowels, I usually just widdle with it knife, pain in the boot for sure.... I also us a pencil sharpner to get a sharp point on the end, then use a rubber mallot to pound it through the cake board.. much easier... and keeps it sturdy for sure... see my photos of the wedding cake, used 3 tiers with dowels done as described. I have also done the bird and banner pan on top of a sheet cake and didn't use a board or dowel. On my 3d duck cake on the sheet, I did use dowels, that puppy was way too wobbly to trust it. I am working on a monster truck this weekend and was given the idea to use foam wrapped in foil for the 3D car pan to give it a boost off of the sheet.... with dowels, so I will see how that goes.. Good luck!
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