If you're talking about locking them up on the ask so nobody can borrow them to short them, it isn't necessary with a cash account. They can only borrow shares from a margin account, so those are the ones to put on the ask and they can go at any amount. Scottrade only allows 5X the current price for cash accounts, and I assume this also applies to margin accounts but you can keep moving it up as the price increases.
The other type of locking them up is buying and holding. If you're not selling any time soon, they're locked up. That's what some people are referring to, locking up the float.
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