I had one done standing too. Kinda. A big drafty 3 yr old. It was done for free by my regular vet at the time, because the vet had not done a flank entry cryptorchid gelding before, and was looking for a guinea pig. We did it at home. He got the horse’s side opened up, and reached in there, fished around some, and said, “I don’t believe this!!!”. He said,“It isn’t there.”. He said that he could find the cord that the other rather large nut was hanging on, no problem. But the other cord was either not there, or, actually, it felt like it was already cut, like a nub of the cord left. So he cut the other side as per normal (standing- almost all Colts I’ve had gelded over the last 4 decades have been done standing unless there was a distinct reason to lay them down- which apparently is a surprise to some on this message board???). Since I had bought the colt from the breeders, and they sold him to me as a ridgeling/cryptorchid, I insisted that he had NOT been partially gelded previously by someone else. So we decided that he had been a “monorchid”, removed the one large and obvious nut, and called him a gelding. But it was an odd day. I sold the horse soon afterwards, so can’t comment on his success as a horse. I kept his half brother who I had bought at the same time, who better suited my needs.