One of the gates had a sign saying to use the attached metal spike to prop the gate open against the first line of raised bricks that were painted yellow. The large log in the lock prevented the gate fully opening and the spike was not going to reach the yellow brick line. I then saw that, log or not, it must often fail to reach the carefully indicated place and in stead there was a small depression in the concrete a few inches away from the yellow brick line, and it had been surround by a small yellow rectangle. The spike fitted in and didn't slip and I could leave it unattended to walk round to the other gate. I intended photographing it and got Shane to pass the camera but two workmen came to operate the lock for their boat, so in stead of going round to that side again, I went down to get back aboard.