Respect is a two way street. Your grandma is not respecting you if she insists on letting her marking, peeing dog to run around your house without a belly band on. I don't think it is at all rude to request that he wears it and you are even willing to provide it. It's not as if you are putting a straight jacket on him. The belly band is not an instrument of torture.
If you're really brave, you ought to print out this thread for your grandma to read. Maybe that will make her realize that she is being unreasonable. Then again, she just might write you out of the will.
