millie210 - jwleaks, how did you manage that sail? That is gorgeous!
In 2009 the local roads department were replacing old timber highway double-sign posts with steel posts. I salvaged as many posts as I could then cut off the rotten section (which is the part that was buried in the ground), paint stripped them, and then gave them a going over with an electric planer and belt sander. Several coats of wood sealer later I concreted the posts in the pool area and attached the shade sail. The cut out features of the posts, i.e. the two round holes and cut line between them, were part of the original posts and were at the height of a car fender and were designed to break the post at the ground level in an accident. I flipped the posts upside and made the safety feature a pool post feature.
The sail is attached to the posts by chain and eyelet with a tensioner between them to take up the slack of the sail. Each post has a different height where the sail is attached thereby creating an angled sail and giving tension. The below picture is the lowest point of the sail / post and is towards the late afternoon sun during summer. The pool is 12 meters in length and is salt chlorinated with a reverse polarity setup. I have a solar heating system for the pool on my shed roof which measures a full 9 meters x 6 meters in size.