re: Cypress knees are getting to be an issue. Recs for taking them down a bit?

I have to cut about 40 each year in the spring. They are at grass level and feel like a cobble stone road going over them. I use an ax for anything over 3" and for knees under 3" I use a Milwaukee 18v cordless drill with a 2 1/4" bit shown below. I usually drill them about 3-4" below grass level. It only takes about 10 seconds of drilling. It is very aggressive but will get used to it after a few attempts.

LINK

I may order a larger one.