I prefer the Zenport garden shears for dividing. A paring knife will work for most clumps, the shears just speed up the process and leave you with less hand fatigue.

I also highly recommend a cut proof glove for your non-dominant hand. This is always the hand that ends up being cut, and we for sure don't have time to be fooling with stitches during the big dig and divide. I use these. I have fairly large hands for a woman, and wear a medium.

For marking tubers, I have not found anything to be more permanent than the Sharpie Industrial Markers. The industrial part is important! I am not sure what the difference is, but, it matters!