I am very familiar with the “don’t make me get up” warning. As soon as one’s tush leaves the chair… it works wonders.

Policy at Maine Coon Manor for keeping cats of counters, bookshelves, and tables is a particular set of stern verbal warnings followed by physical action:

“Cleo, down.”
“Cleo, get off the [name of article of furniture].”
“Don’t make me come over there!”
Getting and walking over to the cat. “Fee, fie, fo, fum, I see the fluff of a ’Coon kitten!”
Gently shove cat off of furniture they’re not supposed to be on.

Usually I only have to get to “Don’t make me come over there!”, or start to get up to show I really do intend to remove them from the furniture, and the cat will jump down.

My wife complains that the cats listen a lot more to my booming “daddy voice” than to hers; sometimes I’ll hear her starting this sequence in another room and add my voice, and the cat will then jump down where they were previously chirping defiance. (Getting back-talk from a cat is just too funny. “Cleo, down!” “Meh-eh!”)

We also have an implicit rule that upholstered surfaces are always okay for cats to be on, and the only non-upholstered surfaces for cats are floors, so they have a tactile association as well as a “which piece of furniture” association.

Controlling scratching works similarly, with the addition that they always get verbal praise for scratching on their scratching post and sometimes get treats.