I agree with Catahula ...
and ususally do something similar. For example, over time:
(1) Go to garage sales, pawn shops, thrift stores, etc. and pay $1-$3 each for some good but old cue cases and some firewood (e-r-r-r crapy cues). Leave the sales receipt, if any, lying around so the wife can find it. Set them in the corner somewhere out of sight (say in your closet or behind a door).
(2) Have a secret stash of cash or a paypal account that the wife doesn't monitor. Again, build it up slowly over time bit by bit each week or month.
(3) Research things and get a really really good idea of what you want. So, when you do buy something it's not just an impulse purchase but something you really want.
(4) When you find what you want, snap it up and replace some of the "firewood" (i.e., burn it, toss it in the trash, give it to your local bar, practice putting tips on it, experiment with cue wax or other things, donate it to a local thrift store, etc.). The basic idea being that the wife probably won't notice the switch since it's in a case and out of sight. (But, if she always watchs you play pool that could be a problem.)
(5) Make sure that if the new cue is being delivered to you that you track the item on it's way to you and either pick up the mail at the post office that day (we have a P.O. Box) or be sure the wife is not around when the UPS or mail truck arrives.
(6) If you get busted, have a plan. For example, if your wife has a hobby, research beforehand what kind of things she would like to have and continually keep asking her if she would like this or that for her birthday, Christmas, etc. Then, if you get busted, you could say you came across this great deal, someone else was going to snap it up for sure and you bought it for yourself for your birthday, Christmas, etc. And, would she prefer to keep it and put it away until then and wrap it as a present for you?
Voila.
.../Woody
P.S.: The separate accounts advice by others is a better and more straight forward approach (especially if your wife has a hobby).
The best way to approach this sort of situation is with what I like to call "the Quorum Approach". This is an approach that I took with my much needed collection of expensive fly rods.
1. you start collecting a bunch of inexpensive rods from your buddies or K-Mart, whatever.
2. you leave them out, openly displayed in a very conspicuous area of the house.
3. make a point of talking about them with your wife and pointing out how little they cost you.
4. once you have 4 or more in the pile you are now approaching "Quorum Level". You can now start replacing those with the real expensive keepers as your wife
will not notice whether or not there are more or less rods over in the corner.
She will just be glad if you clean up the f'ing mess in the corner and stop talking to her about your shit.
This system works wonderfully with any type of expensive hobby, that it is your right as a man, to indulge in.
go forth and enjoy...you are man..hear you Roar!