This thread always reminds me of the seagulls from the movie "Finding Nemo"
Here come the haters.....LOL
I don't think it's reasonable to expect Couples to monitor the usage of every chair. Leave that to the NSA!
As jamaican_junkie pointed out, the selfish in the crowd will likely continue to be selfish no matter what is said to them...it's just in their nature.
We just got back home from CSA a few days ago. Prior to New Year's Day, the resort was at capacity, and we usually needed to cover the length of the beach a couple of times to find two chairs with floaties (not necessarily together). Of course, it was impossible to know what chairs were unoccupied for a short time and what chairs had been unoccupied since 6:30. We would just round up a couple of chairs and floaties and move them to the part of the beach we wanted to be at.
One couple did get under our skin a bit. They had two chairs/floaties under a palapa and a third chair/floatie about three feet away so the guy didn't need to move his chair three feet to switch from sun to shade. And of course 3 towels while the towel hut was empty. Just a touch arrogant.