When I do Fisherman's rib, I knit the first row, then do k1, k1b across the sts ending with a k1. The next row is k2, k1b across and end with k2. I keep repeating these rows which makes it reversible. You could knit all sts on the WS row instead, like the first row. It's tricky to remember to alternate sts, if I have a large number of sts I sometimes get off, knitting 2 instead of k1, k1b.