I put them down with a needle. My horse is 22 now, still working as he can, and when he can't and life is too painful, he'll be put down by my vet. Whether he is buried with a backhoe or taken to rendering after his death, I don't know yet.
He has been too good to people in this life to be betrayed at the end for a few hundred dollars.
I was being general, and I respect your attitude. In fact, you have made me ponder something I never really thought about too much, not owning horses myself; these semi-rural suburbanites with horses, do they ever think ahead about how they are going to handle the situation? I do know that some people acquire horses who are not set up to take decent care of them, and end up having to sell them; the same could be said for lack of foresight even if they were able to provide a good home.