The nut slot on one of my warmoth strat necks is super deep to the point that the strings will buzz off the first fret with a pre-slotted black tusq nut that I haven't even taken a file to yet. I guess I have to shim the slot. I had a bone nut on it, but I prefer using the black tusq overall. What are some recommendations for shimmimg the slot- is there a particular hardwood veneer one would recommend, or is the old business card/sandpaper routine still in vogue?