It might be better to call the credit card issuer BEFORE making such large purchases, if it is not part of your normal buying habits with that card.
I always notify the card issuer for the top 2 cards I use, before making large (like thousands of $ for airline tickets) or before traveling internationally.
I know not all cc issuers notify you when charges are decline, but you should check to see if they can do this. I know most of them let you know when charges over a certain amount have been charged. AMEX even sends emails when the card was not present... of course, I seem to be getting this a lot even when the card was present.