Covered Calls Margin

Under what circumstances do you have to cover a short position?
Suppose you have enough money / margin in your account to cover the share price. Under the circumstances of your broker can make the rug out from under you? I heard more calls margin, there is also a possibility that they will not be able to borrow from anyone any longer for any reason? I'm not sure I understand how this can happen, and how it can be prevented from occurring with a frequency unfair to small, medium type traders joe. TIA!
You are shares held on margin by borrowing from other investors, when a buy-in "is performed somewhere in the position to Long chain.The delivery.depending requires actions to the age of short, and you can have one of the oldest positions, you are required to cover. It has an effect Training on the purchase price of shares covering short well.By you must be "bought". You have no choice, your stockbroker does not trade on the market. If the stock is hot you can be involved in the contraction where there is a short panic buy and the market will very quickly is the risk of short. If you will play the short game, you must have an exit price at different levels to profit:. Very rarely does the stock go to zero, unless they are penny stocks OTC OB.
Trading Conference – Covered Calls – Mark Larson 1/6