I usually see them running nearly parallel to the surf and then later turning back towards the surf. Working the sides of runnels is more productive for me than the bottom.
Had one that opened up on a local beach and I found a 14k band in the bank of the runnel. A few days later there was no evidence that the runnel ever existed as it had filled completely full of sand. Two weeks later it was open again and I found a second 14k band very close to the area where I had found the first one. Good Luck and good hunting