My son helped me with this one - we had concrete wall blocks left from a retaining wall demolition, and thought that recycling them into something useful would be a good thing to do. Just found these pics of the construction (from a couple years ago)
(https://lh3.googleusercontent.com/-skXUh8KEimY/UmFfH1WvvEI/AAAAAAAAEZ8/KE2tKNjq4EU/w1109-h832-no/IMG_0127.jpg)
(https://lh3.googleusercontent.com/-FyjUOFtCtyI/UmFfI1wYG_I/AAAAAAAAEaI/iWs6iqd39xM/w624-h832-no/IMG_0129.jpg)
(https://lh6.googleusercontent.com/-F_qYvcnW32Y/UmFfJDU3vAI/AAAAAAAAEac/HU-aKaeKexs/w1109-h832-no/IMG_0132.jpg)