From what I know it is by invitation only and not a club where u can just call and say hey can I join and stable, unless you are a top high goal patron maybe and will need to buy their horses and hire members of the family for tournaments.
I agree 100% with David, I know quite well Gonzalo Pieres, his sons, sister Rosario, and I had been there late Sunday. Ellerstina isn’t an open club for anyone who wants to keep his or her horses in their stables, only you will find Pieres’ polo ponies and some others from friends and guests. Most family club like this one in Argentine follow the same policy like Dolfina from Adolfo Cambiaso and his family, Aguada from the Novillo Astrada’s family. Pilara is an exception because anyone who is member of the club can have his horses there, is just two kilometres from Ellerstina, the same with Centauros just in front of Ellerstina. These clubs are more similar to clubs like Myopia in Boston, or in Wellington Florida, or Cirencester or Cowdray Park in England, Chantilly and Polo Paris in France. But forget to have any horse in Ellerstina, Gonzalo Pieres senior will never allow people who are not familiar with the family to have horses there, just friends or partners.
You know, I always assumed that Ellerstina, like La Dolfina, operated this way. But at the Ellerstina tournament, there was a field nearby where some very low-goal looking chukkers were going on and I just assumed that they were club members playing. Of course, come to think of it they could have been playing at the club next door, which might be Polo One, but I'm not sure.