I am wondering the same thing. It is a relatively recent dilemma. When I was a kid we would bury our cats and small dogs in the backyard but that wasn't possible for our large dogs. Back then vet offices would offer a service to have your pet cremated but you wouldn't get the ashes back. The cynic in me wonders whether they were truly cremated.
Since they return the ashes nowadays, I have two wooden boxes for my most recently deceased dogs. I keep them safe in a drawer but I don't see them every day. You could leave instructions to have the boxes buried with you when the time comes.