Aaron, I don't think the problem is the paper [I buy my cardstock from Office Depot] but with the marker. Most of them are solvent based and the solvent can wick into the compressed paper fibers pretty quickly. I have had much more luck with acrylic paints [the craft type not the tube type]. They don't seem to have the ability to make that capillary movement [they are too thick and dry a little slower]. Try dipping a #2 or small round brush into water, drying it off, then into the paint, then, using the side of the brush, run it along the edge (from the back side of the piece). I think you will find that it doesn't wick into the paper.
I know this has most likely been beat to death
I am making a sample model and the cardstock I am using bleeds when you use marker on the edge
What is a better type of paper to use?
Thanks
Aaron