One Thing I Don't Understand About the "No-Fly Zone" Idea ...

Hillary Clinton, along with various other American hawks and neoconservatives, keeps publicly mulling the possibility of a "no-fly zone" over Syria.

Left unsaid: The US would either appoint itself and its allies, or get itself and its allies appointed by the UN, as the enforcers of that "no-fly zone."

What I don't understand is this: Why don't the Assad regime and its Russian ally beat the US and its allies to the punch?

Step 1: Assad declares a "no-fly zone" over Syria;

Step 2: Assad announces that his government, and its Russian allies, will enforce said zone with aerial patrols, with the use of surface-to-air missiles, or both; and

Step 3: Just to make sure there are no misunderstandings, Assad explicitly informs the US and its allies that if their planes are seen over Syria, they will be shot down.

Seems like it would be hard for the US to object without at least tacitly admitting that it wasn't really serious about a "no-fly zone" but rather was angling for a "nobody flies except us zone."