RE:RE:made2lastIt all depends upon how many shares are made available for "securities lending" in the marketplace.
The best thing we can do as shareholders is to make sure that if your TLT shares are held in a margin account, that you do not go into a negative cash position because that allows your broker to place your shares on loan (without your consent or knowledge) to whomever wants to borrow them (rent them) for a fee. As an FYI, if your shares are loaned out, you will never know cause they will appear as an asset in your account but they have been loaned out to a shorter. Technically it becomes an obligation of your broker to make your account whole. For example, if you wanted to sell your TLT shares that have been loaned out, your broker would simply take the shares from somewhere else in their system to satisfy your sale. Don't kid yourself, securities lending is a big business for institution custodians/brokers and represents 1/3 of their fee revenue split out as 1/3 direct custodial/trading fees, 1/3 securities lending fees and 1/3 f/x fees on the spreads.
Another way to prevent share from being loaned out of a margin account regardless of the cash position, is to just put them up for on-going sale in the margin account at some very high price i.e. $20.
I don't believe that shares can be loaned out of any registered accounts like RRSP, TFSA RPP etc. so no issue there in terms of your shares being loaned out to shorters.