After all stitches are cast on...and you are going to "join" the two ends...slide the stitch marker onto the righthand needle, and begin to knit off the lefthand needle.
An example of a stitch marker on the needles:
As you approach the stitch marker for Round 2...just slide it off (pass it from) one needle onto the other and move on.
PS: that piece of yarn running under my needle is a "lifeline"...temporarily run under the stitches to mark a 'known row' in case you have to rip the work back. Lifelines are useful for complicated, lacy projects.
Stitch markers can even be little baby's rubber bands.
Or, yarn stitch markers, tied into a circle on a larger needle, knotted, and ends snipped off. I put a dob of glue on the knots and let them dry. It prevents the knots from undoing.