I have a fairly large walk-in gun safe I built in the basement. When I got another gun, it would just kinda blend in with the rest of them and I could claim I always had it, and that she just doesn't pay much attention to what I do.
So, now I order a mortar barrel from Hern Iron Works. I already figure that it won't just blend in, and, since she is home all day (like when the UPS guy comes), a 92# crate won't go unnoticed. Still, I figured I had a coupla weeks before it shows up to think of somethin.
Anyway, I start to realize that keepin 25# or so of black powder in the basement would be a bad thing so, during a warm weekend in January I start unloading concrete bags from my pickup and driving them out into the woods in my camo painted, jacked up golf-cart.
My wife thinks this is odd behaviour, even for me, so she sends my 4 year old son down back to investigate. An hour later he returns, covered with mud, and tells her that it is "top secret", and he won't tell her anything (good boy :-).
A coupla minutes later, there I am shoveling concrette into a 5x5 hole inthe ground out in the woods and she wanders up and asks "What are ya doin?"
I tell her I am building a storage shed for dangerous stuff cuz the kid is startin to get into things. Se says "Your building a dynamite shed, arn't you?". I say... "well, ya... I guess". She is happy, because she had one as a kid (it belonged to her grandpa) and now we will have one too.
So, a coupla days later, on Presidents day (I had the day off), she calls to me and tells me the UPS guy is standing in the driveway looking into the back of his truck and doesn't look happy. I go out, help him move it, and open the crate in the kitchen. By this time, she has been so confused about all the strange happenings (like building a dynamite shack in the middle of the winter), that a little 13 inch chunk of cast iron isn't all that big a deal, and it is possibly a better explaination for the strange behaviour than whatever she was thinkin was happening.
She was even nice enough to pick the barrel up from the machine shop that EDM'ed the fuse hole for me, so I guess she has gotten over it by now.
So, I guess make her think somethin much, much, much, much worse is about to happen, and then she will be relieved cuz all you are getting is a little tiny cannon.
The next one will be only a little bigger. Maybe someday I'll have so many that a new one will just blend in.
BTW, she has a horse too (and I have 10 llamas), so a pattern of commonality may exist between you and me... i.e. ... start pouring some concrete in the woods yourself, as winter is almost over. Offer no good explaination for it... maybe giggle alot for no apparent reason. (The real reason is that the UPS guy will be here any day now).
Good luck.