I sometimes use a different small piece of yarn as a marker. If you are changing colors or need to fine a certain point use a marker. In the round I place a piece for a couple of rounds and just move them up with the beginning of the round. It is like with knitting, use
if you need to or the pattern says to mark it and move it for each row if necessary or pattern change. You can use a marker if you want to for your own as a remainder for you even if the pattern doesn't call for a marker.