good idea, but not all true.
You have an agreement (fine print) with your brokerage house (the discount ones) that allows them to borrow your shares for shorting. Until your sell limit is executed, your shares can be borrowed. You can call them to confirm. I thought the same and in 2008 was trying to push the same with SIRI. I finally did the reasearch, called Ameritrade and read the brokerage agreement.
You have to remember, with a brokerage house, they own the paper stock and sell it to you on their behalf. You have to get the actuall paper stock to stop a short from occuring.
But it is still good to put in a high sell limit to try and pull up the ASK (can't hurt), but none of us have enough shares to have any impact on the price really. Especially with 6 billion shares outstanding at SIRI.
Long SIRI.