I think I’ve got it. My response to Marty will be pretty much the following:
"Marty, I could give you legal reasons why Ford’s ashes cannot be scattered at the farm where he was born, and why you need not honour your agreement with Old Farmer. But I won’t.
Instead, I’ll ask you to think about Ford. Where he lived, how he lived, and what he liked to do.
For most of his life, he lived in your house. You made sure that his food and water bowls were always full. Ford liked sleeping on your couch, and in front of your fireplace. He went outside, and enjoyed your yard, and the park beyond.
Marty, you gave Ford a home; the only home he ever really knew. He likely remembers nothing of his kittenhood, as you and I remember little of our early childhoods. Scattering his ashes at the Farm would mean nothing to him. But in the park, in your yard, he would be at home. You owned him for 16 years, Marty–he is more yours than Old Farmer’s at the old farm. Let him rest on familiar ground."
If Old Farmer would like to be there by Marty for the scattering in the park, great. If he complains, tough. Ford was Marty’s cat. Marty ought to consider his pet over a 16-year-old oral promise, and let Ford lie where he was happy and comfortable.
(And I will buy Marty a beer after the scattering.)