I said paper and pencil, but if you want to take a little time these are great. I've got several in different lengths.
How- I take a bag of jump rings like this and put together as many as I've got pattern repeats. For the last one on there I add a bead or make the marker a different color jump ring from the others.
You place it on your needle not on your knitting, and for each for each row you knit you move down the row of rings by picking up the next one and dropping the first one.
For instance if you have a 5 row repeat (4 knit rows, 1 purl row) you use 5 rings. On the second row stick your needle into the next loop down and keep that one on the needles. When you get to the last one you know that is the row you are going to purl.
I'll see if I can find better instructions, too.
Like this, but I prefer the simple jump rings..this one is too confusing.