Miss Manners: My guests keep putting their feet on my furniture despite my hints

Dear Miss Manners: When visiting my home, friends and relatives sit down and immediately put their feet on the sofa, even though I have a leather hassock for resting their feet sitting directly in front of the sofa.

I recently purchased a new sofa in a dark blue fabric, as I did not want to spot-clean after visits. Other chairs are covered in a lighter-colored fabric. While chatting during a recent visit, my niece stood next to a chair and put one foot on the seat. Her father was seated on a chair with one foot tucked under him, and her mother was sitting on the sofa with both feet curled under her.