You need to hunt down a copy of Patric McManus' article on the art of Running Guns Past Your Wife. It's hilarious and quite useful. some of the tips I remember are:
First, the MOST important thing is to never let her count them. So long as she simply asks "What do you need all those guns for?", you are OK. The day she says "what to you need 17 guns for?", you are sunk. Make sure it stays "all those" and never a number.
* Give that gun you just bought to a trusted friend. Have him drop it off some evening thanking you for loaning it to him for a hunting trip.
* Hide the new gun you just bought. Every couple of weeks take a part off and come in through the front door with it exclaiming to your wife what a great deal you got at the swap meet, or from the gunsmith's junk table.
* Have an expandable gun rack. Whenever you add to your collection add to the rack so the last 3 slots are always empty.